Diseases Associated with a Black Skin Rash in Dogs

By Betty Lewis

Yikes! Your dog is losing his hair and developing a black skin rash. The problem may be as simple as flea infestation, or it may be hormone-related, such as alopecia X. Diagnosing the cause of his black skin rash can be tricky, and involves blood tests, urinalysis and occasionally, a skin biopsy. Some breeds, such as poodles, Alaskan malamutes, chow chows and Siberian huskies, are vulnerable to the black skin rash known as alopecia X.

Flee, Flea

The first thing to do if you notice some hair loss or what looks like a black rash on your dog is to take a close look at what else is happening. His black skin rash actually may be fleas and their dirt. A dog with a severe flea infestation will have little black bits of flea excrement in his hair, as well as fleas actually crawling around on his skin. He'll likely scratch and bite at the fleas, trying to get some relief. Hair loss, scabs and hot spots can develop in extreme cases, and a dog with flea allergy dermatitis will show an extreme reaction to just a few fleas. Your vet can prescribe an effective flea topical to keep fleas at bay. You'll have to thoroughly clean your house, including vacuuming all areas your pup frequents and potentially fogging the house to ensure the parasites are gone for good.

Black Crusty Skin Disease

If your dog isn't infested by fleas, he may be suffering from black crusty skin disease, otherwise known as alopecia X or pseudo-Cushing's Syndrome. The first symptom of black crusty skin disease is often hair loss. Typically, the dog's hair loss is symmetrical, shedding from his torso and the rear of his back legs. In most cases, the hair on his head, neck and front legs is normal and his skin usually will turn black.

The Reason for the Rash

The hair loss in black crusty skin disease is hormone-related, which is also often the case with hypothyroidism and Cushing's disease. Because all three conditions can show similar symptoms, it's important to have the vet verify the reason for your dog's rash. Diagnosis can be tricky, so your vet will order blood work, testing for thyroid and adrenal function, as well as a urinalysis and possibly, a skin biopsy. Normal thyroid and adrenal functions can help confirm a diagnosis of alopecia X.

Alopecia X

If your pup has alopecia X, the cause may be a low level of growth hormone. Growth hormone can be used to treat the disease, however, it must be used carefully and under a vet's supervision as it can lead to diabetes. If sex hormones are the culprit behind his black crusty skin, neutering is often effective at solving the problem. If he's already been neutered and his hormone levels are normal, the vet may recommend to leave the condition be, as it's a cosmetic issue instead of a health concern. Medication, such as melatonin, trilostane and ketoconazole, can help address the condition, but your vet will decide if a prescription medication is best for your pup.

Cushing's Disease and Thyroid Irregularities

Thyroid irregularities and Cushing's disease also may cause hair loss and black skin rashes on a dog. Cushing's disease may present additional symptoms, including faded coat color with a dull, dry appearance, as well as a pot belly, small blackheads on the abdomen, listlessness, infertility, increased thirst and urination, weakness and loss of muscle mass. Symptoms of hypothyroidism include weight gain, lethargy and intolerance to cold. If your pup is diagnosed with either Cushing's disease or thyroid problems, the vet will recommend a treatment protocol.