Hair loss or alopecia can be due to a variety of causes. In cats it is most commonly self-induced whether due to psychogenic factors or pruritus. A visit to your veterinarian can help determine if the hair loss is self-induced. Your veterinarian can pluck a few hairs from the alopecic region and examine it under a microscope to determine if they have been chewed out. The most common reasons for pruritic hair loss are flea/tick hypersensitivity, food allergies, and environmental allergies. Psychogenic issues as the underlying cause for hairless is much less common and often over diagnosed when the correct underlying cause can not be determined. Circular patchy areas of hair loss can be due to ringworm which is due to a fungus. Ringworm is more common in young kittens, geriatric, and immunocompromised cats.
Correctly diagnosing the most common underlying cause for pruritic hair loss takes a lot of time and very strict effort. A flea/tick hypersensitivity trial will require use of a flea and tick preventative every 2 weeks for at least 4 treatments before determining its effectiveness. A food trial will require a completely new food with a novel protein and carbohydrate source. Many over the counter limited ingredient foods are not truly limited ingredient and the labels must be read with extreme caution. Prescription hypoallergenic foods although costly are a much more reliable source of limited ingredients. Your cat will need to be placed strictly on this new diet with no other food of any kind for a minimum of 2 months before assessing if there has been at least 50% improvement. If there is 50% improvement, then the trial should be continued. If there is less than 50% improvement the trial can be discontinued. All food sources need to be reviewed carefully as people often forget about things such as pill pockets and treats that can completely disrupt the food trial. Environmental allergy testing can consist of a blood test or intradermal testing. Pending the results of these tests cats can be started on customized allergen immunotherapy vaccines. These vaccines require consistent use and results may not be seen for up to one year. Failure of these vaccines can only be determined after a year. Some owners who do not see results from any of the above mentioned will go for immunosuppressive medications such as Atopica. Immunosuppressive medications also have their side effects so careful consideration should be given before starting any of these medications.
Cats who truly have hairless due to psychogenic issues can be started on anti-anxiety medications prescribed by your veterinarian.
Certain rare types of hairlessness can be due to much more serious disease such as pancreatic cancer. It is therefore very important to have any hair loss examined and discussed with your veterinarian.