Parasitic Allergens

Many - perhaps nearly all - dogs with atopic dermatitis (AD) are hypersensitive to parasite allergens, irrespective of their other sensitivities. In particular, sensitivity to fleas is common. This is one allergen source that can be largely eliminated! A foundational part of treatment for canine AD is parasite control. All dogs with AD should remain on regular, monthly parasite control measures to prevent, to the extent possible, flea infestations from becoming established. The newer parasiticide regimens will often control other parasite sources as well, such as scabies or Demodex mites.

Food Allergens

Though much less common than environmental allergies, food allergies can be a part of the canine AD picture. In fact, we recognize that the clinical signs of canine AD can, in some cases, result entirely from food hypersensitivity. Some authors have used the term "food-induced atopic dermatitis" for this clinical picture. In other cases, food allergens can be one component of multiple sensitivities in a patient, including environmental allergens as well. Dermatologists' opinions differ on how common food sensitivities are in causation of AD. Some believe that as many as one-third of dogs with clinically diagnosed AD can have some component of food allergy as part of their disease. Regardless of the exact numbers, it is important to evaluate every dog with AD for a food allergy component, through use of carefully performed dietary restriction-provocation trials.

Another element of diet that may be important in some dogs is the possible presence of storage mite allergens in the diet, including such species as Acarus, Tyrophagus, and Lepidoglyphus. These free-living mites feed on stored grain sources, which may include improperly stored dog food. Again, this is an area of some controversy. On the one hand, serologic or intradermal testing to the storage mite allergens is often positive in dogs with AD. Because these mites are closely related antigenically to house dust mites such as Dermatophagoides, one argument is that positive tests to storage mites merely represent cross-reaction with dust mite allergy. But what about dogs that have positive reactions to storage mites, but are negative to dust mites? These patients exist. So, it seems that at least in some cases, dogs can be sensitized to storage mites. On the other hand, several studies have attempted to examine how frequently dry pet food is contaminated with storage mites, and the answer seems to be "not very often." So how these storage-mite-allergic dogs actually contact the mite allergen is not easily explained. What does all this mean practically? Because we know that it is at least possible for dogs to be allergic to storage mite allergens, dry dog food, treats, etc. should be stored in tightly sealed bags or plastic containers to prevent mite contamination as much as possible.

Environmental Allergens

Environmental allergens are the central problem in most dogs with AD. It is important for the owner to understand that the problem allergens cannot practically be avoided. Unlike with food and parasite allergens, with environmental allergens our efforts are not to eliminate the allergen, but to reduce the patient's sensitivity to the allergen with immunotherapy or drug treatments.

Dust Mite Allergens

Sensitivity to house dust mites is the most common problem worldwide in canine AD. Dust mites are prevalent throughout the world and are impossible to eliminate completely. Special measures such as air filters, special cleaners, special beds or pillows or vacuums are sometimes recommended for people with dust mite allergy, but even with extensive study, it is not clear that these measures are very helpful for reducing the severity of disease. The most helpful method of reducing dust mite hypersensitivity is allergen-specific immunotherapy, using either allergy "shots" or allergy "drops."

Pollen Allergens

Second only to dust mite, pollen allergens are also important in many parts of the world. Grass, weed, and tree pollen allergens vary in how important they are, depending on the local climate and vegetation. Also depending on geographic location, these allergens may be seasonal or year-round.

Mold Allergens

It seems that mold allergies vary substantially in dogs, mostly depending on the geographic location. In some areas of the world that have particularly humid or damp weather, mold allergies may be very common in dogs; in other areas, they are uncommon.

Insect Allergens

The prevalence of insect allergy in dogs is not well studied. In urban areas, it has been reported that cockroach sensitization is frequent.

Things that are Not Important as Allergens

Equally important to discuss with owners are the things that are not very common or important, at least in most dogs. Epidermal allergens (sensitization to cats, human dander, etc.) are not common in dogs, nor is allergy to things such as furniture stuffings, fabrics, carpets, rugs, tobacco, and the like.

Microbial Allergens

There has been recently renewed interest in the possible contribution of microbial hypersensitivity to the pathogenesis of canine AD. Clearly, there is a close relationship between AD and skin infections, both with Malassezia yeast and with Staphylococcus. Many studies in human AD have demonstrated that people are often sensitized to yeast or staphylococcal allergens. The same has been reported in dogs, though we are not yet sure how common this is. Complicating the picture is that hypersensitivity to microorganisms can be either immediate-type (IgE-mediated) or delayed-type (cell-mediated). Our current "allergy tests" detect only IgE-mediated, immediate-type hypersensitivity - so it's possible that current testing methods do not accurately report sensitivity to these microbial allergens.

Contact Allergens

Because contact allergy to items such as jewelry, leather dyes, latex, chemicals, perfumes, soaps, cosmetics, etc. is relatively common in people, many owners assume the same is true in dogs, and sometimes go on a search to make sure that their pet's environment is "allergen free" and that they are washing the pet's bedding in hypoallergenic detergent, etc. In reality, exactly the opposite is true - it is exceptionally rare for a dog to be sensitive to contact allergens. In this case, it's a matter of owner education. Owners must be assured that almost all allergy occurs from "things that blow around in the air" or foodstuffs, rather than things the dog is contacting. The exception, of course, would be things like grass allergy, where walking through or lying in grassy areas may easily provoke a reaction.