What to Do When Your Cat Is Sick: ALLERGIC DERMATITIS

The Classic Comprehensive Handbook of Cat Care

What to Do When Your Cat Is Sick: ALLERGIC DERMATITIS

Some cats, like some people, are born with a predisposition to develop reactions when exposed to certain substances in their environment. Cats with allergic dermatitis usually develop skin disease characterized by signs of itching, such as biting and scratching the skin, when exposed to the material to which they have become allergic. In some cases there is no evidence of itching, but other skin abnormalities occur.

Exposure to the substance may be by inhalation (this route of sensitization is common in a form of allergy called atopy), ingestion (e.g., food allergies), inoculation (flea bites, drugs), or direct contact of the skin with the offending substance. You will usually see reddening of the skin, small bumps, oozing and possibly sticky areas and scabs, and sometimes dan drufflike scales. The reddened skin may feel abnormally warm to the touch.

In neglected cases there is hair loss, large areas of raw skin may develop, and the skin may even become thickened. If these changes go untreated long enough, they can become permanent. Areas where scratching is severe may become infected. Cats with allergic dermatitis may lick at their flanks, abdomen, and the inside of their rear legs excessively when grooming, causing a characteristic symmetrical hair loss unaccompanied by any actual skin changes. Cats with this form of allergic dermatitis must be differentiated from those with other (e.g., hormonal) causes of hair loss that take a similar pattern. In addition to skin signs, cats with allergic dermatitis may have more general signs of allergy such as a watery nasal discharge and sneezing, tearing, and conjunctivitis. Some may even have vomiting or diarrhea.


Fleas are probably the most common cause of allergic dermatitis. If you practice good flea control, you may be able to prevent the dermatitis from developing or relieve a case that has already developed. Be careful, however, about putting flea sprays or dips on an irritated skin; they sometimes make the irritation worse. If you think you are controlling fleas but your cat continues to scratch, there can be several possibilities.

For example:

  1. The bite of a single flea (which you may not see) can cause extreme itching in an allergic animal.
  2. Cats can be allergic to many things other than or in addition to fleas— among them pollens, house dust, molds, trees, wool, foods, cigarette smoke.
  3. The condition may not be allergic dermatitis (for an example).


Frequent bathing (every one to two weeks) helps to control the signs in many cats and also helps prevent secondary bacterial infection. It removes allergens from the coat and seems to relieve some of the skin inflammation associated with allergic dermatitis. Use a gentle hypoallergenic shampoo (for example, castile shampoo, baby shampoo, or a veterinarian-prescribed shampoo, not bar soap or dishwashing detergent) to avoid additional damage to a sensitive skin. If your cat’s skin and hair become too dry with bathing, an emollient oil diluted with sufficient water to avoid leaving the fur excessively greasy can be used as a final rinse. Hypoallergenic bath oils for people are satisfactory, or a veterinarian can prescribe a product. If you find that bathing makes your cat’s signs worse, don’t, of course, continue to use it as a treatment.

Often, once the itching has begun it continues even if you remove the original cause of the irritation. This may be due to scratching, which releases itch-causing substances from the damaged cells. When such a cycle occurs, a veterinarian must administer and/or prescribe drugs such as antihistamines, antiinflammatory fatty acids, or corticosteroids to control the problem. In many allergic cats drug treatment must be repeated intermittently or administered continuously.

Skin testing, blood testing, and hyposensitization (induction of immune tolerance by the injection of small amounts of allergen) as used in people with certain allergies have been helpful in some cats with allergic dermatitis induced by environmental allergens such as pollen, molds, and house dust. Special elimination diets, often based on rice or potatoes and lamb, turkey, or rabbit, are useful to diagnose and treat allergy signs related to food sensitivities. A minimum of four weeks’ diet restriction is needed to rule out food-induced allergy. Many veterinarians have a special interest in skin disease and can make an effort to find out what allergies affect your cat. Cats with very difficult allergy problems can be diagnosed and treated by a veterinary dermatologist. For persistent problems, ask your veterinarian for a referral to a specialist.