Allergic skin disease is one of the most common reasons for veterinary visits in dogs. Some dermatologists estimate that up to 40 percent of the dog population will develop some form of allergic dermatitis during their lifetime. For owners this condition can be very frustrating as there often is no definitive cure, and treatment can be ongoing throughout their pet’s life. So it is important for dog owners to have some knowledge concerning their dog’s skin allergies.
First of all, the three most common forms of skin allergies in dogs are flea allergy dermatitis, food allergy and atopic dermatitis.
With flea allergy the dog becomes sensitized to a protein in flea saliva. The area of the body most affected is the rear half of the dog, especially the rump and down the back legs. Luckily, with the introduction of effective topical and oral flea control medications, we see a lot less of this condition than in the past.
Dogs with food allergy become sensitized to a protein in the diet. This could be chicken, egg, beef, lamb, wheat etc. The most common areas affected are the ears and feet, but over time large areas of the body can become involved. A majority of dogs with food allergy also have some bowel problems. Food allergy is diagnosed by introducing a novel protein diet, or a hydrolyzed diet where the protein is broken down so the body does not recognize it. If the itching resolves then the offending food is fed again to see if itching returns. This is done because a change of season or other factors might be what is responsible for reduced itching. Food allergy is not as common as many people think.
With atopic dermatitis the offending allergens are often airborne and include pollens, molds and house dust mites. As with food allergy, the ears and feet are commonly involved. Other areas of involvement are the face, axilla, groin, and in general hairless areas of the body. Unlike food allergy, symptoms of atopy almost always begin in the first 2 years of life. One way to look at atopy is “hay fever of the skin.” In the beginning most atopic dogs exhibit symptoms seasonally, but may have symptoms to some degree year round; they may be worse in the spring and the fall. Atopic dermatitis is the most common form of allergic dermatitis we see in dogs.
Whatever the form of allergy, the result is itching. And this leads to biting and scratching, which frequently results in skin infections with bacteria and/or yeast. The skin infection, in turn, makes the itching worse. So we have a vicious cycle of itching, scratching, infection, followed by more itching. Changes of the skin in the ear canal caused by atopic dermatitis and food allergy often result in ear infections. In fact, the most common cause of ear infections in dogs is allergy.
So what can we do?
- Since sarcoptic mange (scabies) often mimics both food allergy and atopic dermatitis, in severe cases it is prudent to rule out scabies. This is difficult to do with skin scrapings as the mites are very difficult to find. So often we end up treating with the topical flea medication Revolution, since it will treat this form of mange.
- We need to determine if secondary infection is present. If so this needs to be treated by antimicrobials or topical medications or both. Many dogs will need weekly medicated baths to prevent recurrence of infections.
- If the itching is year round a food trial is warranted.
- Flea control. Dogs with allergic dermatitis of any variety cannot tolerate flea bites, so they should be kept on year round flea control medication. Two excellent flea products are Bravecto, a pill given once every 3 months, and Revolution, a monthly topical spot on treatment. Both of these are unaffected by frequent bathing.
- Frequent bathing with a hypoallergenic shampoo. This can help to rinse off airborne allergens and reduce itching. An example of a hypoallergenic shampoo is Vet Solutions Aloe and Oatmeal.
- Fatty acid supplementation. Fish oil capsules containing Omega 3 fatty acids can help reduce itching.
- Many dogs will also need medication to help control itching. Our choices here is corticosteroids (e.g. prednisone), antihistamines (e.g. hydroxyzine, diphenhydramine), cyclosporin (Atopica), and a new medication Apoquel. Unfortunately, antihistamines are usually not very effective but it can be helpful to give diphenhydramine (Benadryl) at bedtime as it helps with sleep. Probably the most significant advance in medication for allergic skin disease over the past 20 years is the drug Apoquel. We have not seen side effects with this medication, and we can use it either short term or on a long term basis. The problem has been supply as this drug is difficult to manufacture and the demand has been very high. The supply is getting better and we are now placing new patients on this medication.
- Immunotherapy for atopic dermatitis. In severe cases, allergy testing by either skin tests or blood tests can be performed; the goal is to develop a vaccine to desensitize the dog. The vaccine can be given by injection or an oral formulation. This can be very helpful but is a long term treatment and results may take some time. Expect more on this in a future blog posting.
Carl D. Anderson DVM