This skin disease is caused by an allergic skin reaction to a number of possible allergens, including the bites of fleas, mosquitoes, mites, and lice. Bacterial and fungal skin infections, nutritional disturbances, hormonal imbalances, autoimmune diseases, and drug reactions can also produce miliary dermatitis. The affected cat breaks out along her back and around the head and neck with small bumps and crusts about the size of millet seeds beneath the haircoat. There may or may not be itching.
Flea bite allergy is the most common cause of miliary dermatitis in cats. Other skin parasites, allergies, and infections should be considered for cats who have miliary dermatitis without fleas.
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The typical appearance of a cat with flea-bite dermatitis: small crusts, bumps, and raw patches of skin, and hair loss due to licking and scratching.
The skin is severely itchy and may break down, producing raw patches that become infected from intense scratching. Localized or generalized eosinophilic plaques may develop as a consequence. A few cats are especially resistant to flea bites and can harbor many fleas without symptoms, but in the allergic reactor a single bite once or twice a week is sufficient to produce the response. Symptoms are most prevalent in the middle of summer (peak flea season). However, once the cat is exposed, if fleas live in the house, itching may persist year-round.
The diagnosis is suspected by seeing the characteristic skin rash and by finding fleas on the cat. You can check for fleas by standing your cat over a sheet of white paper and brushing her coat. White and black grains of sandy material that drop on the paper are flea eggs and feces. The diagnosis is confirmed by an intradermal skin test. This is a hypersensitivity reaction of both immediate and delayed type; itching tends to persist long after fleas have been destroyed.
Treatment: When fleas are present, treat the infestation. In the absence of fleas, an effort must be made to determine the cause of the miliary dermatitis and to treat accordingly.
While treating for the fleas, cortisone tablets, such as prednisone, or injections that block the allergic reaction and relieve the itching are sometimes needed to make the cat comfortable. Steroids should only be given under veterinary guidance. Antihistamines and omega-3 fatty acids may also help to reduce the inflammation. Treat sores with a topical antibiotic/steroid ointment. Aloe ointments or an aloe plant’s juice are also soothing and safe. If the cause of the allergy can be determined and eliminated from the cat’s environment, such as removing all feather pillows, that would be ideal. However, this is not always possible. Hyposensitization (using injections of flea allergens of increasing strength to desensitize a cat’s immune system) can make cats much more comfortable but requires multiple, long-term therapy.
WebMD Veterinary Reference from "Cat Owner's Home Veterinary Handbook"