New Study On Ethoxyquin

A major new four-year research  study has been completed which  determines the effects of ethoxyquin on dogs and their puppies. The study was started in 1991, and results were expected to be released to the Food and Drug Administration during the summer of 1995.

The study used a protocol approved by the Food and Drug Administration. Our research scientist looked at the protocol, and she said the study design meets all current scientific standards.

Monsanto, maker of Santoquin® ethoxyquin, sponsored the study. The research was conducted by an independent testing laboratory.

This expensive piece of research should provide a basis to judge the safety of ethoxyquin in dog food. Another study, part of the National Toxicology Program, is in line for government funding. This study will look at ethoxyquin’s safety for pets and people. No timetable has been set for the start of the study.

But it may be a moot point by the time the FDA releases the study or the National Toxicology Program acts: marketing pressures (not scientific research) has deemed ethoxyquin as ‘”bad,” and nearly all major manufacturers of pet food have switched from ethoxyquin to alternative preservatives.

Ross Becker, 1997

Preservatives Fight Cancer

If you think antioxidants (preservatives) aren’t good for you or your dog, read on.

According to an article in R&D Magazine, Andrew Dannenberg of Cornell Medical College has made an important discovery. He found that antioxidants BHA and BHT boost levels of a natural cancer-fighter. Laboratory animals were used in the tests, but these preservatives seem to have the same effect in humans.

BHA and BHT are antioxidants that are widely used in human and pet food. They “revved up” the gene for an enzyme that helps destroy carcinogens before they trigger tumors. In other words, they caused the gene to produce more of the enzyme which provided better protection against cancer-causing substances in the environment.

ETHOXYQUIN: More scientific data

In the last article we brought you most of the scientific data from laboratory tests of ethoxyquin –tests required to meet the registration requirements for agricultural use of ethoxyquin. From the data presented, one might assume that if dogs were fed several thousand parts per million of ethoxyquin in the diet, problems might occur. But the reality is that your dog, on any commercial dog food, is getting as little as 10 parts per million, and as much as 100 ppm. Now we’ll finish up with the data from the EPA.


The EPA requires tests on chemicals to see what their impact is on the unborn. In particular, teratology looks at whether a significant dose of the chemical will cause an imperfect fetus.

The two laboratory animals usually tested are rats and rabbits. Rabbits usually will abort an imperfect fetus, while the rat tends to resorb it. Together, they represent the reactions of most mammals.

According to the Registration Standard for ethoxyquin, the EPA didn’t find any one report which totally satisfied their teratogenic guidelines. However, there was enough other data on rats and rabbits to satisfy the EPA as to the teratogenic potential of ethoxyquin.

Telford, et al, reported that a single dose of 0.25 grams of ethoxyquin was given to rats after they were confirmed to be pregnant. Twenty days after a positive mating, the pregnant rats were killed. The young were delivered by Caesarian surgery. There was no difference between the group given ethoxyquin and the control group, where no ethoxyquin was given.

In another study by Isenstein, rabbits were fed 600 parts per million (ppm) of ethoxyquin beginning ten days prior to breeding. The rabbits were fed the ethoxyquin until 14 days after the young were born, to include the period of nursing. Again, there was no difference found between the offspring of rabbits fed ethoxyquin and those which were not fed the substance.

Reproduction Studies

The EPA requires at least one study of a mammalian species, preferably the rat, to test the effect of the substance on at least two generations. Studies were found using rabbits, rats and chickens.

While the EPA felt that none of the studies individually met all the requirements for a reproduction study, the reviewers felt that collectively there were sufficient data. The reasons why some of the studies didn’t fully meet the reproduction test requirements included the animal used, the fact that other ingredients were fed to the animals, or insufficient details were given to make the study a meaningful report.

For example, one study on rats involved feeding them 250 ppm and 5000 ppm in a diet that was made to be slightly deficient in Vitamin E. The study continued for two generations. It was concluded that ethoxyquin did not interfere with reproduction in rats.

On the contrary, it was noted that ethoxyquin increased reproductive efficiency (larger litters), possibly because the diet was marginally deficient in Vitamin E, and there is a known symbiotic relation-ship between Vitamin E and ethoxyquin.

Several other studies used the same and higher levels of ethoxyquin: 125, 250, 375, 1000, 1125, and 5,000 ppm. No adverse effects were found – the ethoxyquin caused no interference with the reproductive capacity of the animals tested, even at these very high levels. (FDA limits ethoxyquin usage to 150 ppm in the finished product.)

Again, while none of the studies could stand alone and meet all of the government’s requirements for a reproductive study, it was felt that the information they collected certainly indicates that ethoxyquin does not interfere with reproduction.


Metabolism studies show how the substance is utilized as it goes through the digestive tract, where it is used by the body, and where it is passed through. The EPA’s minimum data requirement is for a study where a single dose of radioactively “tagged,” analytically pure ethoxyquin is given, and followed as it works its way through the body.

Studies were found using rats, dogs, and cattle as test subjects. The studies using rats and cattle showed that ethoxyquin was excreted in the urine and feces.

The study with dogs showed that the labeled ethoxyquin was excreted in the urine, and 85% of it was excreted as a metabolite. (A metabolite is what’s left after it has been metabolized.)

The material in this article and the previous one covered all of the data which could be found regarding the safety of technical grade, 95% thoxyquin. This is the very high-quality kind of ethoxyquin. Ethoxyquin also comes in emulsifiable concentrates, which can be mixed with water. It’s like making orange juice from a frozen concentrate. Scientific data for the 70% ethoxyquin emulsifiable concentrate are very similar to that for the 95% technical grade, and the substance is considered by the EPA to have a very low acute dermal toxicity. The acute inhalation test also showed no ill effects, nor did any of the other studies of the substance.

While some dog breeders have been quick to label ethoxyquin the culprit for genetic defects, reproductive failures, hair loss, and even skin problems around the nose, there is no scientific evidence at all to support these allegations.

In fact, when the EPA reviewed over 500 scientific studies of ethoxyquin, they concluded ethoxyquin is safe.


Telford, I.R.; Woodruff, C.S.; Linford, R.H. (1962) Fetal resorption in the rat as influenced by certain antioxidants. American Journal of Anatomy 110:29-36.

Isenstein, R.S. (1970) Ethoxyquin in rabbit feed: study of relationship to abortion and early neonatal death. American Journal of Veterinary Research 31(5): 907-909.

Ethoxyquin: You Be The Judge

 The Scientific Data and How To Understand It

In the last section we discussed both sides of the ethoxyquin controversy. The breeders said the preservative is responsible for skin problems, kidney problems, and litters born with birth defects or stillborn. The dog food manufacturers and Monsanto, maker of ethoxyquin, claim the stuff is safe, but offered no solid evidence. We concluded that more scientific study was necessary.

Then we found it. The report that provides the answer to the question of ethoxyquin’s safety.

Ethoxyquin is an antioxidant. It keeps fats from spoiling, and has been used in dog foods and animal feeds for over thirty years. As the protein content in a dog food increases, so does the need for fat (so the protein can be assimilated). Incorporation of fat into a diet means preservatives are needed, which usually means either a combination of BHA and BHT, or ethoxyquin.

Ethoxyquin is used as a preservative in chicken, horse, cattle, and pig feeds, as well as dog and cat food. It is also used to preserve the ingredients of many animal feeds, including fish meal and rendered fats like poultry fat. Further, it is used as a preservative for certain dehydrated for-age crops such as alfalfa. It is also used in paprika and chili powder to preserve the red color.

To Interpret, You Must First Understand

We’re about to provide you with the scientific data you need to make your own decision about the safety of ethoxyquin. But first, you need to know how to interpret it. So here’s a review of scientific methods, and a crash course in understanding the meaning of scientific research.

The goal of scientific research is to explain, predict, and/or control phenomena. The goal is based on the assumption that all events in the universe are orderly and that their effects have discoverable causes.

Progress towards this goal involves the acquisition of knowledge and the development and testing of theories or hypotheses. The existence of a viable theory greatly enhances and facilitates scientific progress. This is so especially when com-pared to other sources of knowledge such as experience, anecdotes, inductive and deductive reasoning.

Of all the sources of knowledge, the scientific method is undoubtedly the most efficient and reliable. Let’s compare these different methods.

The problems of using experience and anecdotal information as a method of understanding is best illustrated by a story about Aristotle.

One day the great philosopher Aristotle caught a fly. He carefully counted and recounted the number of legs on the fly. From this study, he concluded that flies have 5 legs. At that time, no one questioned the great wisdom of Aristotle. For many years to come, his findings were uncritically accepted as the truth. As it happened, though, the fly Aristotle had caught was missing a leg. Whether you believe this story or not, it shows the limitations of relying on personal experiences and anecdotes as an authority or source of knowledge. Stories you hear “through the grapevine” or from someone’s experience may contain a germ of truth, but will not be “reliable” in the scientific meaning of the word – the same result occurs every time an experiment is conducted.

Inductive and deductive reasoning also have their limitations when used as a single source of knowledge.

Inductive reasoning involves the formulations of generalizations based on an observation of a limited number of specific events. For example: Every dog book contains a chapter on canine nutrition. Therefore, all dog books contain a chapter on canine nutrition.

Deductive reasoning, on the other hand, involves the reverse process: arriving at specific conclusions based on generalizations. For example: All dog books contain a chapter on canine first aid. This book is a dog book. Therefore, this book contains a chapter on canine first aid. (Does it?)

None of these approaches are entirely satisfactory. However, when used together, as integral components of scientific research, they can be very effective. The scientific method involves induction of hypotheses based on observation, deduction of the implications of the hypotheses, the testing of the implication, and confirmation or disconfirmation of the hypotheses.

The scientific method is a very orderly process entailing a number of sequential steps: recognition and definition of a problem, formulation of a hypothesis, collection of data, confirmation or disconfirmation of the hypothesis.

These steps can be applied informally to everyday situations to determine such things as which route to take to this week-end’s dog show … the best time to go to the bank drive-in window … the best crate to purchase. The more formal application of scientific methodologies to solutions is what scientific research is all about.

Scientific research is the formal, systematic application of an experimental method to the study of problems. Basic scientific research is conducted for the purpose of theory development and refinement. Applied scientific research is conducted for the purpose of testing or applying a theory and evaluating its usefulness in solving a particular problem.
In other words, basic research pro-vides the theory that produces a possible solution to the problem. Applied research provides the data to support or disprove the theory, guide revision of the theory, or suggest the development of a new theory.
The experimental method is the only method of research which really tests a hy-pothesis in a cause-and-effect relationship. It represents the most valid approach we have to solving scientific questions, both practical and theoretical, and to advancing human knowledge.
In all experimental studies, the researcher manipulates the independent variable (who gets what; which group of subjects get which treatments) and controls other relevant variables, observing the effects on one or more dependent variables. The effects on the dependent variables are measured.

The independent variable is also referred to as the cause or the experimental variable. It is the activity or characteristic believed to make a difference. Generally, all other factors will be held equal or constant, so a cause and effect relationship can be established.

The effect is seen as the dependent variable. The dependent variable is the outcome of the experiment which is dependent upon the independent variable. It is measured by an analytical test or method to produce reliable data. When conducted properly, the experimental variable is demanding and most productive. It produces the soundest evidence concerning hypothesized cause/effect relationships. The findings of an experiment permit predictions to be made about the cause and effect relationship.

Analytical testing and methodologies are used to ensure the reliability and validity of each measurement of the dependent variable. Reliability is the degree to which a test consistently measures what it is supposed to measure. You might call it the degree of trustworthiness or dependability. The higher the reliability of a test, the more reliable the data.

Validity is the degree to which a test measures what it is supposed to measure. Many people think that a test is either valid or not valid. The truth is, a test may be valid for a particular purpose or experiment, but not for another. The question is not “Is it valid?”, but valid for what and for whom?

There are two basic requirements for any experiment. First, the method should lead to decisions regarding the reliability of the analytical data. Second, the decisions should be related to the purposes for which the analyses are being done.

The final judgement regarding the reliability of the data and validity of the analytical test or method is made on the basis of one question: Have consistently precise and accurate short and long-term biochemical data been provided?

An experiment should end with decisions regarding not only the analytical significance of the data but also the significance of the control data. Control samples must be analyzed and handled in the same rigorous way as the experimental samples. Data from both control and experimental samples reflect changes which occur in the analytic test itself. With two sources of data – control and experimental – the researcher can select the most effective method of analyzing the data to arrive at a reliable and valid conclusion.

Back to Ethoxyquin

Now that you know what to look for in an experiment, and how the scientific method works, we can ask the big question about ethoxyquin. Do we have consistently precise and accurate biochemical data, both short and long-term, on the toxico-logical effects of ethoxyquin to determine its safety?

The answer is yes, we have the data to determine its long- and short-term safety. But don’t take our word on it. Armed with the preceding basic lesson in scientific research, you can draw your own conclusions based on the information and data which follows.

Many articles published by others on ethoxyquin informed you that so-and-so did a scientific literature search to see if there were any adverse effects on animals. So and so’s findings were that no adverse effects were found. Other articles stated that someone else found evidence that ethoxyquin may be beneficial as an anticancer agent … and some said the FDA says it’s safe, therefore it must be safe. Yet other articles mention that ethoxyquin, when fed at extremely high dosages, showed it may have a cancer-causing potential. One article even went as far as discussing ethoxyquin’s effects on slowing down the aging process.

Quite frankly, that information is all well and good, but it doesn’t provide you with the information you need to know. None of the statements you just read are relevant to the question at hand: Is there precise scientific data on the toxicological effects which determines the safety of ethoxyquin?

Research on the carcinogenic potential of ethoxyquin, where it is fed well in excess of the toxic level, has nothing to do with determining the safety range of the substance. Research on anticancer properties of ethoxyquin has nothing to do with it either. Nor does anyone’s opinion on ethoxyquin’s safety really matter. All this information is nice to have, but it does not answer the question. Nor does it provide you with the hard-core scientific data that you need to make your own decision.

In order to answer the question you must review the published scientific studies relevant to the question of toxicity. If a study is not relevant, then it has no business being discussed as other than supplemental materials. It should not be used as part of your decision making process, nor in your conclusion. Unfortunately, until now there has not been any pertinent research available for you to look at.

When looking at literature and data, you’ll want to separate it into three basic categories. The first is studies which con-tribute useful information on ethoxyquin’s toxicity. This is the information you’ll need to determine how safe or unsafe ethoxyquin is in your dog’s diet.

The second category of studies are those examined and judged to be inappropriate for use in developing a database. These may be poorly conducted studies, or just plain irrelevant to the question at hand.

The third category is standard reference materials relating to the reliability and validity of analytical tests and methods. These allow you to determine whether the methods used to analyze the experimental results fall under the category of frequently used, reliable and valid tests.

In the following pages we will provide you with the relevant data on the toxicity of ethoxyquin. All of this information falls within the realm of “good scientific research.” The analytical methods and data are reliable, repeatable and valid. We have eliminated the irrelevant or invalid studies from this discussion.

Our telling you what we think is no different from any other “expert,” and we are certainly not going to be an Aristotle claiming that flies have five, not six legs. We encourage you to read on, and make your own conclusions.

Where the Information Is  From … And Why No One Told You About It Before!

At the beginning of this article, we mentioned ethoxyquin’s use in dog and cat food, plus chicken, horse and pig feeds, paprika and chili powder. There’s one other use of ethoxyquin: as a scald control on apples and pears. Many have misunderstood this use, calling it a pesticide. But that’s not true.

Commercially sold apples and pears, like much fruit, are picked “green” – before they ripen. The fruit is hard, and is better at surviving the bumping around on the way to the marketplace.

When fruit ripens, it goes through an oxidizing process which gives off ethane gas. The ethane gas speeds ripening. If the ripening occurs too soon, the fruit develops brown spots, also called scald.

Drench the fruit with an antioxidant, and the ripening process slows down, preventing those unsightly brown spots. That’s why ethoxyquin (e.g. 3000 parts per million – ppm – for 2 to 3 minutes) is used. By the time it reaches your store, there is no more than 3 ppm. on the fruit. (Alternatively, wax used on apples, and paper used for shipping pears and apples, will contain ethoxyquin to slow the ripening process.)

It was this use of ethoxyquin which led us to information most dog food companies didn’t know about, and neither Monsanto nor the Food and Drug Administration pointed us to-ward. You see, because of this agricultural use, ethoxyquin is regulated as a pesticide, even though it isn’t really used as a pesticide. The federal agency which keeps a tight rein on pesticides is the Environmental Protection Agency (EPA), and that’s where we found all of the following information.

The EPA took over pesticide regulation from the U.S. Department of Agriculture, and routinely reviews applications for registration of new pesticides. Traditionally, a new pesticide would be reviewed application by application, each independently. This way the pesticide could be judged safe or not for each use.

This method left little opportunity to combine information into a “big picture” of the safety of a particular chemical. So the EPA revised their procedures to look at the overall safety of each chemical, as well as the individual uses.

The EPA and Congress also spotted another problem: many pesticides had been registered before the advent of modern scientific methods, and were being sold and used without any current assurance of their human and environmental safety. Ethoxyquin was one such product, having been invented in the 1920’s.

Congress mandated that the EPA re-register all previously registered products, and required that the database for each be brought up to current standards. The new procedure is called the Registration Standard.

The Registration Standard contains all the information on a particular product:. This includes its active ingredients, current uses, conditions and requirements for registration, existing and future products which contain the active ingredient, all required scientific data. Also included is a discussion on compliance with government standards on toxicity, composition, labeling, packaging and the reliability of the data.

In 1981 the EPA put together the Registration Standard for ethoxyquin.

A Minor Use Chemical

In its review, the EPA classified ethoxyquin as a “minor use” chemical. This means that in the preceding five years, less than 30,000 pounds of the chemical’s active ingredient were used in formulated products.

Data Required

The EPA required data on the physical and chemical properties as well as acute toxicity for all ethoxyquin products. We’ll explain these in more detail later.

Results of tests were required for the technical grade of ethoxyquin (95% pure active ingredient) and the emulsifiable concentrate (a liquid concentrate to be diluted) which comes in 52.2%, 59.0%, 65.5% and 70% ethoxyquin concentrations. In this article we’ll use the data for the technical grade of ethoxyquin – the 95% pure chemical. Data for the emulsifiable concentrate reflect similar findings.

Manufacturers and formulators of ethoxyquin products supplied data on ethoxyquin’s chemistry, residue chemistry, and toxicology. Data was also required for other ingredients in the formulation, active or not, which constitute 0.1% of the product by weight. This allows for a good evaluation of the toxicity of the ingredient up for registration, and helps to complete the “big picture.”
All data was reviewed to insure that it met the EPA’s standard of scientific methodology. Most met the standards, but some studies were thrown out. The information in this article came from studies which met the standards.


When a chemical is submitted for registration for use on food, each of the fol-lowing kinds of studies must be submitted:

1. Chronic Feeding. A two-year feeding study is done using rats. Controlled amounts of the chemical are fed to the rats, and an autopsy is done at the end of the study to determine the effects.

2. Cancer. Oncogenicity studies are required from each of two suitable species of mammal. For ethoxyquin, rats were used in this test to see if the material causes tumors.

3. Teratogenicity testing, performed in two species of mammals, is designed to see whether the chemical causes abortion or reabsorption of the fetus. Two species are tested because some mammals will reabsorb the fetus, others are more likely to abort.

4. Reproduction. A two-generation reproduction study was required, preferably in the rat. This tests litter size, the survival rate of babies, growth, and liveborn vs. stillborn.

5. Mutagenicity. Tests are conducted to see if cells are damaged or mutated. Other tests are checked to see whether the DNA has been changed or damaged.

6. Metabolism. A general test to see how the chemical is metabolized in one mammalian species. The purified substance is labeled with radioactive material and followed through the animal’s system. Monitoring is done to see what organs it visits on its journey through the body.

Other studies are required, such as Acute Inhalation Toxicity, Skin Sensitization, and Subchronic Oral Toxicity. We’ll take each of these one by one and explain them, then look at what the study of ethoxyquin found.

One of the purposes of these studies is to determine at what level the chemical causes illness. Just about every substance will cause some problem, if given in high quantity.

Long-Term Feeding Studies

One chronic, or long-term feeding study, preferably in rats, is required to check for toxicity – to see whether the substance is toxic, and if so, in what amounts.

The EPA reviewed eight studies on rats and chickens, where technical grade, 95% pure ethoxyquin was fed daily in concentrations ranging from 62 ppm to 15,000 ppm, for a period ranging from 50 weeks to 2 years.

(Where appropriate, we’ve converted all measurements into parts per million (ppm) a unit of concentration, for easy comparison. The maximum concentration allowed in finished animal foods is 150 ppm, and far less is generally used. No matter how much food is consumed, the ppm – the relative amount of ethoxyquin – will remain the same.)

Wilson (et al) found that rats receiving 2000 ppm of ethoxyquin for over 200 days had problems. When autopsied, male rats had lesions in the kidneys, whereas females had none.

At the end of the study (715 days total) rats given this high dose exhibited a transient depression in growth rates. Instead of showing steady growth, they would grow sporadically. Male rats had lesions in the kidneys, livers and thyroids. Females had no lesions.

Obviously, 2000 ppm caused problems for the male rats. But the study also tested the 620 ppm concentration of ethoxyquin. There were no observable effects. A study by De Eds (et al) confirmed that there was no observable effect on rats at 620 ppm.

Panner and Packer did a two year feeding trial with rats, with the control rats being given 100 ppm of ethoxyquin, and the experimental rats 15,000 ppm. Only 11% of the rats fed the 15,000 ppm survived the entire two years. The high level of ethoxyquin caused both visible and microscopic changes in the livers.

Rudra (et al) reported that 5000 ppm of ethoxyquin fed to weanling (just weaned) male rats for 500 days, causes a slowing in weight gain, and severe kidney damage.

Colorado A&M University reported the effects of 75 ppm and 750 ppm fed to chickens for 70 weeks. They found no effect on growth of the breeding flock.

Gassner (et al) also did a 70 week chicken study, feeding 7.5 ppm, 75 ppm, and 750 ppm in the diet. They found no significant effects on mortality, growth, feed consumption, livability, egg production, fertility of eggs or hatchability which could be ascribed to the ethoxyquin.

What does this mean? From this data, one might assume that if your dog were to get several thousand parts per million of ethoxyquin in the diet, liver, kidney and thyroid problems might occur. But the reality is that your dog, on any commercial dog food, is getting as little as 10 ppm and as much as 100 ppm. Even at seven times the amount, one would not expect any illness.

Tumor Formation

The EPA found only one oncogenicity study discussing the presence of tumors and ethoxyquin. In rats fed 62 ppm and 2000 ppm for 715 days, an occasional tumor was found at day 700. The EPA found fault with this study because 700 days is a long time for a rat to live, and rats that age commonly have tumors. Further, the study didn’t link ethoxyquin to the tumors, and didn’t describe the relationship between tumors and the dose level.

Acute Oral Toxicity: How Much Ethoxyquin is Lethal?

One scientific number to look for is the LD50. The LD50 is the median (av-erage) dose which killed 50% of the test animals in the study.

The LD50 for ethoxyquin indicates that the amount required to be fed to cause damage is very high – 21 times the normal usage. The LD50 in rats is 3,150 ppm (Kellman, G.Y., 1965).
In mice the LD50 is 3000 ppm (Kell-man, G.Y., 1965) and in chickens the LD50 is 8000 to 10,000 ppm (Colorado Agricultural Research Foundation, 1951.) We have not found any studies which determine the LD50 in dogs, probably because no one is willing to do a study which intentionally kills dogs.

Is Ethoxyquin Toxic if Inhaled?

The EPA requires one acute inhalation toxicity test with the albino rat. Rats were exposed for 6 hours to 1750 ppm of 95% pure ethoxyquin and observed for 14 days. An autopsy revealed no visible damage, no ill effects.

Skin Sensitivity

Allergies often show up in skin sensitivity. The EPA requires an interdermal test in one species of mammal, preferably the guinea pig. Ethoxyquin was injected under the skin. The guinea pigs showed no sensitivity, no allergic reaction.

Short Term Feeding Studies

The EPA requires at least one sub-chronic oral toxicity test – a short-term feeding test – in two species of mammal. Eleven studies of this kind were analyzed by the EPA. Seven looked at ethoxyquin and rats, three used chickens, and one checked the effects of ethoxyquin on lambs.

Whanger (et al) found that 500 mg of purified ethoxyquin, fed three times a week to lambs, exceeded the LD50 – lambs died. Unlike the other studies discussed in the EPA report, Whanger fed straight ethoxyquin. When the dosage was cut back to 250 mg three times a week, there were no deaths.

Colorado A&M University fed Monsanto’s Santoquin® brand of ethoxyquin to chickens for 12 weeks, at levels ranging from 150 to 15,000 ppm of the diet. There were no effects on body weight, feed consumption, or livability, and the liver, spleen, kidney, thyroid and testes remained normal.

Conclusions of the EPA

“Ethoxyquin as described in the standard may be registered for sale, distribution, reformulation and use in the United States.” Based on all of the scientific data on ethoxyquin from the worldwide scientific literature as of 1980, plus the data submitted by the registrants through the time of the standard’s publication in 1981, the “Agency finds that none of the risk criteria found in section 162.11(a) of Title 40 of the U.S. Code of Federal Regulations have been met or exceeded by ethoxyquin, and that ethoxyquin does not appear to cause an unreasonable adverse effect with proper label directions and precautions.”

In other words, ethoxyquin exceeded all safety standards of the law. The EPA considers ethoxyquin a low toxicity chemical, and very safe.

The maximum level allowed by the EPA is 3 parts per million of ethoxyquin residue in or on apples and pears. The FDA allows a maximum of 150 ppm in finished animal feeds and dehydrated forage; most dog food contains far less.

The difference in the regulated amounts has more to do with the purpose for which ethoxyquin is being used. It takes far less ethoxyquin to prevent bruising of fruit than to keep fats from going rancid.


Colorado Ag. Research Foundation (1958). Chronic Toxicity of the antioxidant 6-ethoxy-2,2,4-trimethyl-1,2, dihydroquinoline.

Gassner, F.X.; Buss, E.C.; Hopwood, M.L.; Thompson, C.R. (1960). Effect of feeding 1,2, dihydro-6-ethoxy-2,2,4, trimethylquinoline to chickens. Poultry Science 39:524-533.

Gordon, R.S.; Machlin, L.J. (1952). Determination of minimum dietary level of Santoquin® which produces no more than .1ppm residue in dog and monkey liver: Ratio to greatest possible human consumption of Santoquin and calculation of safety factors. EPA Registration Standard MRID#00001932.

Hadley, K.G. (1965). Summary of Test Residues From Ethoxyquin Treated Pear Wrap. EPA Registration Standard MRID#000002198.

Hanzal, R.F. (1955) Chronic Oral Administration in Dogs: Metabolic Studies. Hanzal Laboratories. EPA Registration Standard MRID#000001925.

Jung, H.D. (1975). Professional dermatoses in agriculture of agricultural and industrial district of Neubrandenburg, East Germany. Deutsch Gesundheistwesen 30, 39: 1540-1543.

Kahl, R; Netter, K.J. (1977). Ethoxyquinas an inducer and inhibitor of Phenobarbital-type cytochrome P-450 in rat liver microsomes. Toxicology and Applied Pharmacology 40(3):473-483.

Kellman, G.Y. (1965). Comparative Toxicity of Santoflex AW and acetoaniline. Crude and Vulcanized Rubber I:24(3):40-41.

Koziak, B; Sesevick, L. (1971). Eczema produced by contact with poultry feed mixtures. Occupational Medicine 23(7):240-244.

Netter, K.J.; Kahl, R.; Elcomb, C.R. (1978). Significance of induction phenomena. Archives of Toxicology, Supplement (1):85-99.

Parke, D.V.; Rahim, A.; Walker, P. a) (1973). Reversibility of hepatic changes caused by Ethoxyquin. Biochemical Society Transactions 1(6):1316-1319.

b) (1974). Biochemical Pharmacology 23(13): 1871-1876.

c) (1974) Inhibition of rat hepatic microsomal enzymes by Ethoxyquin. Biochemical Pharmacology 23(24): 3385-3394.

Pascal, G. (1974). Physiological and metabolic effects of antioxidant food additives. World Review of Nutrition and Dietetics. 19: 237-299.

Rudra, D.N.; Dickerson, J.W.T.; Walker, R. (1975). Long-term studies and some antioxidants in the rat. Journal of the Science of Food and Agriculture. 25(8): 1049-1050.

Takahashi, O.; Hiraga, K. (1978). The relationship between hemorrhage induced Butylated hydroxytoluene and its antioxidant properties or structural characteristics. Toxicology and Applied Pharmacology. 46 (3): 811-814.

Wilson, R.H.; De Eds, F. (1959). Toxicity studies on the antioxidant 6-Ethoxy-1, 2-dihy-dro-2, 2, 4-trimethyl-quinoline. Journal of Agricultural and Food Chemistry. 7 (3): 203-206.

Wilson, R.H.; Thomas, J.O.; Thompson, C.R.; Launer, H.F.; Kohler, C.O. (1959). Absorption, metabolism and excretion of the antioxidant 6-ethoxy-1, 2-dihydro-2, 2, 4-trimethyl-quinoline. Journal of Agricultural and Food Chemistry 7(3): 206-209.

Ethoxyquin: The Full Story

In 1989 and 1990, ethoxyquin in pet foods first became an issue. Here’s what we published back then.

Elaine Campbell is a respected breeder of Collies. She asserts that ethoxyquin caused allergy, immune system and reproductive problems with her dogs. Her suspicions first brought the ethoxyquin question into the limelight.1

Elaine Campbell told us, “My dogs’ problems have all been eliminated by changing the food. The change to health was also rapid and widespread. Nothing else has changed but the food,” she says.

She had been feeding a dog food imported from Canada. When tested, a batch showed 202 parts per million of ethoxyquin. The U.S. limit is 150 parts per million, but products imported to or exported from the U.S. are not checked regularly to see if they meet U.S. standards.

On the industry side, Purina spokes-man Patrick Farrell states, “Purina produces approximately 19 canine foods, only a few of which contain ethoxyquin, and at levels much less than 150 parts per million. There have been no complaints about ethoxyquin over the years.” Purina feeds are tested in lab studies as well as feeding trials. They currently employ over 1000 dogs of a variety of breeds.

The dog world is abuzz with “The Ethoxyquin Controversy.”

Why Use Ethoxyquin?

The fat in a dog food is not only the primary energy source in the food, but is also the source of fat-soluble vitamins A, D, E, and K. Fats are also the source of a critical nutritional element: fatty acids.

But fats can go bad – turn rancid. Rancid fats have undergone partial decomposition or oxidation. Rancid fats can make the food smell bad and taste awful. They will also cause the decomposition of the fat-soluble vitamins, biotin and essential fatty acids.

Ethoxyquin is an antioxidant. It prevents rancidity.

Ethoxyquin is present today in a lesser or greater degree in virtually all animal feeds, including cat food, poultry feeds, processed horse feeds, livestock feed and dog foods. It has come into widespread use, especially since other antioxidants such as BHA and BHT came under increased scrutiny. But the history of ethoxyquin goes much farther back.

Ethoxyquin was invented in the 1920’s, and patented in England in 1939. Later, Monsanto researched its uses as a preservative for fats and animal by-products.

In 1956, ethoxyquin was approved by the FDA (Food and Drug Administration) as a feed grade antioxidant.2

Ethoxyquin can be added to animal feeds in one of several ways. It can be added to animal fat at the rendering plant, or it can be sprayed on to feed after the cooking process, when fat-soluble vitamins are added back to the food. But it also shows up in other ingredients the manufacturers buy, such as poultry meal and animal by-products. So even if it’s not listed on the label, it is probably in the food.

Ethoxyquin is approved as an additive to animal feeds, but not to human food, except for uses in paprika and chili powder. Because it is in animal feed, the FDA allows a certain amount of residue to show up in meat and poultry.

Dr. Robert Schisla is a scientist with ethoxyquin’s manufacturer, Monsanto Agricultural Company. He has been working on ethoxyquin since the mid-1960’s. He explained, “At the same time ethoxyquin was up for review in the 1950’s, BHA and BHT were going through the approval process for human foods. It was felt that there was no sense in testing ethoxyquin (for human use), as the market need would already be filled.”

In 1958 the Food Additive Amendment to the Food, Drug and Cosmetic Act was passed. It established a list of additives without known hazards, the Generally Regarded as Safe, or GRAS list. These are additives which have been used for some time, and are only reviewed if there is sufficient question about their safety. They can be removed from the list if necessary.3 BHA and BHT are on the GRAS list, as is ethoxyquin.

How Much Is Used?

Ethoxyquin is a very efficient antioxidant and stands up to processing well. The FDA’s approved use level is 0.015% of the finished product or 150 parts per million. That is the maximum safe level the FDA allows in animal feed.

According to Joe Palermo, Business Manager for Ethoxyquin at Monsanto, most American dog food companies “typically use 75 to 100 parts per million to provide the necessary antioxidant ‘power’. Monsanto recommends a maximum of 125 parts per million. But, from an economic standpoint, you won’t find companies using more than they have to, as it’s a very expensive ingredient.”

The amount of ethoxyquin in all animal feeds is directly related to the protein content of the food. A higher protein content increases the energy need. If that need is supplied by fat, there is an increased need for a higher level of antioxidants.


Ethoxyquin was approved for use in animal feeds in 1956 on the basis of a one year test.

The study found that 3 milligrams of ethoxyquin per kilogram of body weight, 5 days a week for a year was a safe dose.

But equally important, “Microscopic changes in the liver and kidneys were ob-served in dogs receiving dosages of 10, 50 and 100 mg/kg (of body weight) per day. Due to the toxicity of the test material, dosing at 100/mg/kg was discontinued after 6 weeks.”4 Many chemicals, vitamins and minerals are safe at low levels but not at higher levels, so this is not surprising.

The “Secret” Study

Between 1959 and 1964 Monsanto Agricultural Company conducted a long-term safety study in dogs. This study was not required for FDA approval, but was undertaken by Monsanto to further validate the results of their one-year study.

Dr. Schisla of Monsanto told Good Dog! “This study has not been released to the general public as part of corporate policy. This holds for all Monsanto products, not just ethoxyquin.”  This kind of study is considered to be proprietary information.

Various dog food manufacturers we have talked with, including some who use ethoxyquin, have also been unable to get the study from Monsanto. Even the FDA did not see it until they specifically requested it in 1987.

Despite the fact that Monsanto refused to provide Good Dog! with their study, and the FDA told us they didn’t have it, we acquired a copy of the study which had been requested under the Freedom of Information Act.

The FDA said the “five-year study in dogs (1959-1964) by Monsanto Agricultural Company of St. Louis, MO, found no pathological changes attributable to ethoxyquin.”5 That’s a good conclusion, and bears out the idea that ethoxyquin is safe.

The Experiment

The experimental design of the Monsanto study would not meet today’s standards, as research standards have become much more stringent over the last 25 years.

The beagles in the study were kept in group pens. Dogs managed to chew through collars and fences, mixing experimental dogs with control dogs. Both hepatitis and distemper ravaged the colony, a common occurrence before the development of modern vaccines.

Planned and unplanned litters resulted from the group living. Some puppies were added to the experiment, but others died before weaning due to problems attributed to inbreeding.6

The FDA’s Response

In 1982 the FDA Center for Food Safety and Applied Nutrition conducted a literature search and concluded that there was no evidence of ethoxyquin being a carcinogenic (cancer-causing) agent.

In 1988 a second literature search found a 1987 paper which suggested a carcinogenic potential at ridiculously high dosages. Because of this, the FDA nominated ethoxyquin for toxicity testing in the National Toxicology Program. “A decision on whether this testing will be undertaken is expected to be made late in 1990,” the FDA said.7

What Dog Owners Say

A spokesperson for the FDA told Good Dog! that the agency is receiving many phone calls about ethoxyquin. Most are from people with questions, but some are reports from people having problems with their pets. These include allergies, skin problems, cancer and immune system problems, signs of liver conditions, and reproductive difficulties. Because these are observations, as opposed to clinically substantiated reports, the FDA cannot act directly on them. But they do collate such reports, and this can stimulate further research.

We Need More Research!

Further research can validate and substantiate the claims about the use of ethoxyquin in dog food. No one, for example, has checked to see if certain breeds or types of dogs are more sensitive to ethoxyquin (as, for example, Collies are with the heartworm drug Ivermectin.)

The technological revolution that occurred in the early 1980’s would lead one to think that the manufacturers of ethoxyquin would want to duplicate their previous studies with present-day procedures and controls. The development of the science of pharmaco-epidemiology (the statistical study of the long-term effects of drugs within the population) suggests that an epidemiological study be conducted too.

Further, a long term toxicity and tolerance study should be conducted at an independent site, such as at two universities or veterinary colleges, or the proposed National Toxicology Program study. While testing of this nature is expensive, Good Dog! has already heard from one dog food manufacturer willing to assist in funding an independent study on ethoxyquin. We think the time for these kinds of studies is now.


We have more questions than conclusions. But here is a summary of the facts

As far as we can determine, there is no such thing as an ethoxyquin-free commercial dog food. Trace amounts show up even when food manufacturers don’t add any to their food – it’s in the meat, byproducts and fat they buy. Dog foods which add ethoxyquin are supposed to list it on the ingredients.

The FDA approved the use of ethoxyquin in 1956 prior to any long-term tests.

The 1959-1964 Monsanto study had many weak areas in terms of modern scientific methods. (We understand that Monsanto is considering undertaking a new, improved chronic toxicity test in dogs.)

Most companies who use ethoxyquin use less than the FDA’s maximum approved amount. These lower levels seem to be doing a perfectly satisfactory job of preventing oxidation.

Everybody seems to agree that ethoxyquin is very good at its job, preserving fats and other ingredients in foods.

Something is affecting the dogs, and we don’t know what it is..

We still have many, many unanswered questions.


 1.    Campbell, E. “Ethoxyquin – Friend or Foe?” New England Obedience News 5/19/1989.
2.    Monsanto Release. “Ethoxyquin Facts.” 6/1989, Monsanto Agricultural Co., 800 N. Lindbergh Blvd., St. Louis, MO 63167.
3.    Technical Details Report. “Additives in Pet Food”. Fall, 1989. Hill’s Pet Products.
4.    Monsanto Material Safety Data.
5.    FDA Talk Paper. “FDA Review Finds No Adverse Health Threat From Ethoxyquin”. 11/2/89, Food and Drug Administration, U.S. Dept. of Health and Human Services, Public Health Service, 5600 Fishers Lane, Rockville, MD 20857.
6.    “A Five Year Chronic Toxicity Study in Dogs With Santoquin.®” 1964. Available from the Freedom of Information Act Office.(Santoquin® is a Registered Trademark of Monsanto Agricultural Company for their brand of ethoxyquin.)
7. FDA Talk Paper, 11/2/89.

Our thanks to those who generously gave of their time to help make this article complete: Elizabeth Hodgkins, D.V.M. of Hill’s Pet Prod-ucts, Midge Guerber, The U.S. Food and Drug Administration, Dr. Robert Schisla and Joe Pal-ermo of Monsanto Agricultural Company, June Wholley, Elaine Campbell and Carol Barfield.