Allergies are very common causes of dermatitis or skin rash. Seasonal inhaled allergies are called atopy, which usually shows up as red, itchy areas on the paws, face, armpits, and groin. Food allergy can also show up as dermatitis frequently on the head and neck. Allergies to flea bites most often show up as an itchy rash around the rump and tail.
Some rashes are caused by the buildup of moisture. So-called “hot spots” can pop up seemingly overnight as moist, red, weepy areas skin under matted fur. Usually some irritation (eg, a flea bite) sets off licking, which keeps the skin moist, which creates an environment suitable for bacterial growth and formation of a hot spot. Obese dogs and certain breeds (eg bulldog, Shar Pei, and pug) have folds in the skin that also create moist environments that favor the growth of bacteria. Skin-fold rashes are found most often in the folds around the face, lips, armpits, groin, and mammary glands.
Fungi, which are also called dermatophytes, can infect hair, nails, and dead skin, leading to bald, scaly areas with broken hairs. These areas can show up as patches or rings (which are more common in cats), leading to the informal name of ringworm. Infection with mange mites causes red, scaly skin that may or may not be itchy, depending on the specific type of mange mite involved. Dogs and cats can also develop non-itchy skin rashes from certain types of seborrhea.
Treatment for skin rashes depends on the underlying cause and the severity of the problem. Hot spots and skin-fold infections are usually easily treated with cleaning and topical medications, although the underlying cause may still need to be addressed. Flea allergy dermatitis requires thorough flea control to eliminate the cause of the rash. Inhaled allergies usually require seasonal treatment with corticosteroids and antihistamines, and/or more costly and time-consuming hyposensitization shots. Specific medications are available to treat ringworm and mange mites; sometimes it is necessary to also treat unaffected pets because these conditions are potentially infectious. Oral antibiotics may be needed to control secondary bacterial infections associated with any skin rash.