Dr. Stephen White, a professor of dermatology at the University of Califorina, Davis, School of Veterinary Medicine, answers this week's question.

Question: My cat has been losing hair in abnormal amounts for six months. She either tugs at it or licks it. I changed her dry food to grain free, but it hasn't seemed to make a difference. It isn't fleas. What can I do to provide her some relief?

Answer: There are a number of reasons why a cat is uncomfortable enough to pull out its own hair.

This may be caused by allergies (flea, food or environmental, such as allergies to house dust mites or pollens) or to certain parasites or fungi.

The most common cause of this discomfort (the medical term is pruritus, or the sensation of 'itch') is a flea allergy -- the more allergic a pet is to fleas, the LESS likely the owner is to see fleas on the pet; only a small number of fleas biting the animal will continue the allergy (which is from the proteins in the flea's saliva, injected in to the pet while feeding).

However, if we assume that either fleas are not the problem or that the owner has the cat on good quality flea control, then the next step is twofold:

-- Have the veterinarian scrape your cat's skin for parasites and perform a fungal culture to rule out a dermatophyte ('ringworm') infection.

-- Start a hypoallergenic diet trial. Unfortunately, there is no intrinsic value of the 'grain free' diets.

A hypoallergenic diet must be performed using a protein source the pet has not eaten before. These diets are best obtained through a veterinarian's office; most of the diets marketed for allergic pets in pet stores or supermarkets contain a number of different proteins.

Such a diet should be the only thing fed (plus water) for two months, without any treats, chewable medications, flavored toothpastes or flavored toys.

It is important in cats to monitor the palatability of the diet, as cats that refuse a new diet for several days can become seriously ill.

To avoid these problems, the old diet can be mixed in with the new one for the first week. After two months, the pet should be fed its old diet again. If the itching/pulling out of the hair decreases on the hypoallergenic diet, and becomes worse on being fed the original diet, than the pet has a food allergy.

If not, and if all skin scrapings and fungal cultures have proved to be negative, most likely the cat has environmental allergies and should be referred to a specialist for further evaluation.

Dr. Stephen White

White has worked as a veterinary dermatologist for more than three decades, becoming a Diplomate of the American College of Veterinary Dermatology in 1983. A 1979 graduate of UC Davis School of Veterinary Medicine, he did his internship and residency at Davis as well. He held faculty positions at Tufts University School of Veterinary Medicine and Colorado State University College of Veterinary Medicine and Biomedical Sciences, before joining the School of Veterinary Medicine at University of California at Davis as a full Professor in 1998. White has lectured throughout the United States, Canada, Europe, and Asia. He has published over 80 journal articles. His areas of major interests include cutaneous manifestations of systemic disease, rabbit/rodent dermatology, nonsteroidal therapy of autoimmune disease, congenital skin disease, and equine dermatology.