When your dog has allergies

What is an allergy?

An allergy is the immune system reacting to something in the environment. The substance causing the reaction is called an allergen. Dogs can be exposed to these allergens via the respiratory tract (by breathing), digestive tract (by eating), and absorption through the skin (through direct contact).

An allergic reaction is different from a typical immune response because in the case of allergies, the immune system is reacting unnecessarily to what should be a harmless substance. 

What are the signs that my dog has allergies?

Itchiness is one of the most common signs of allergies. The itching can be generalized (all over the body) or can be localized (in just one area of the body). Swelling and redness of the skin may also be observed. Some dogs have allergies that impact their digestive function, leading to diarrhea or vomiting.

Common types of allergies, diagnosis and treatment

The three most common types of allergies in dogs are atopic dermatitis, flea allergy dermatitis (FAD), and food sensitivities. Allergies can co-occur and often do; for example, dogs that have atopic dermatitis are also more likely to have FAD or food allergies. This can sometimes complicate diagnosis and treatment.

Atopic dermatitis

Atopic dermatitis (atopy) is when any allergen, such as dust, pollens, and/or molds, cause a skin reaction. Itching may occur all over the body, but the feet, face, armpits and groins are commonly affected. If the dog is allergic to certain pollens or molds, itching may be seasonal. Dogs usually show first signs of developing an allergy between 6 months and 3 years of age.

Management is usually lifelong, and may include medications, shampoos, allergy shots (immunotherapy), dietary changes, and supplements. If the cause of the allergy is known, avoiding exposure to the allergen (such as by using air filters, or by wiping down your dog with a moist cloth after walks) can also reduce signs. 

Atopy is a diagnosis of exclusion; other skin diseases must be ruled out. 

Flea allergy dermatitis (FAD)

When dogs are allergic to proteins in a flea’s saliva, they will often experience local itching from a bite. FAD typically leads to itching on the lower back, near the tail, and on the back legs. Some dogs may itch to the point of broken skin, which can result in a secondary infection.

Even one flea can set off an allergic reaction, so it is important to keep your dog up to date on monthly flea control, and also treating the home environment to keep it flea-free. In some cases, dogs may need antihistamines or corticosteroids to control itching, and antibiotics to control any secondary infections.

Note: Some dogs will react to other insect bites, such as from flies, mosquitoes, hornets, and ants.

Food sensitivities and allergies

Not every adverse reaction to a food or ingredient is an allergy, although dogs can have intolerances to food. If the immune system is involved in a reaction to food, then it is considered an allergic response. Dogs with food allergies are most often allergic to proteins in the food, such as those from beef, dairy, chicken, and wheat. Signs of food allergies including itching, respiratory distress, and sometimes digestive issues such as frequent soft stool, diarrhea, or vomiting. 

Diagnosis of food allergies usually starts by doing a food trial (also known as an elimination trial). The dog is exclusively fed a hypoallergenic diet (commonly a hydrolyzed or a novel protein that the dog has not previously eaten) for the trial period (usually a few months). Then ingredients that may have caused the adverse reaction are reintroduced. If the dog’s symptoms improve during the trial, but return after ingredients are reintroduced, it is likely that the dog is allergic to those proteins.

Management of food allergies requires feeding a diet that meets a dog’s nutritional needs but does not contain any of the ingredients that caused the allergic reaction.

Immunotherapy

Immunotherapy (usually in the form of injections) can be used to increase a dog’s tolerance to allergens, by slowly and gradually increasing their exposure to them. Immunotherapy takes several months to reach full therapeutic effect, and dogs typically need careful monitoring as well as management for allergy signs during this time. Over time, many dogs experience a reduction in itching and other signs. Although it is the preferred treatment for many allergies, immunotherapy cannot cure allergies. 

Heritability/breeds at risk

Any dog can develop allergies. However, it is believed that allergies may be heritable, because parent dogs with allergies are more likely to produce puppies with allergies. Some breeds appear to be more susceptible to allergies, including Chinese Shar-Peis, Golden and Labrador Retrievers, Dalmatians, Boxers, Boston Terriers, Lhasa Apsos, Scottish Terriers, and Shih Tzus.

Dogs (and it turns out, their owners) in urban environments are also at higher risk for developing allergies.

Allergies and breeding decisions

Because allergies are likely genetic, you should consult with a veterinarian before breeding a dog with known allergies. Breeding decisions should consider the severity of the allergies, the overall health of the dog, and other factors such as genetic diversity and temperament.

Resources and references

VCA: Allergies in Dogs

VCA: Atopic Dermatitis (Atopy) in Dogs

VCA: Food Allergies in Dogs

VCA: Flea Allergy Dermatitis in Dogs

Carlotti, D. N., & Jacobs, D. E. (2000). Therapy, control and prevention of flea allergy dermatitis in dogs and cats. Veterinary Dermatology, 11(2), 83-98.

Hakanen, E., Lehtimäki, J., Salmela, E., Tiira, K., Anturaniemi, J., Hielm-Björkman, A., ... & Lohi, H. (2018). Urban environment predisposes dogs and their owners to allergic symptoms. Scientific Reports, 8(1), 1-9.

Hill, P. B., & DeBoer, D. J. (2001). The ACVD task force on canine atopic dermatitis (IV): environmental allergens. Veterinary Immunology and Immunopathology, 81(3-4), 169-186.

Mueller, R. S., Olivry, T., & Prélaud, P. (2016). Critically appraised topic on adverse food reactions of companion animals (2): common food allergen sources in dogs and cats. BMC veterinary research, 12(1), 1-4.

Nuttall, T. J., Marsella, R., Rosenbaum, M. R., Gonzales, A. J., & Fadok, V. A. (2019). Update on pathogenesis, diagnosis, and treatment of atopic dermatitis in dogs. Journal of the American Veterinary Medical Association, 254(11), 1291-1300.

Verlinden, A., Hesta, M., Millet, S., & Janssens, G. P. J. (2006). Food allergy in dogs and cats: a review. Critical Reviews in Food Science and Nutrition, 46(3), 259-273.