Alopecia is the partial or complete lack of hair in areas where it is normally present. Hair loss is a sign, and its underlying cause must be determined in order to be treated. If a cat has hair loss and is scratching the area excessively, the itching problem should be investigated first.

Hair loss can be congenital (present at birth) or acquired. Congenital hair loss may or may not be hereditary. It is caused by a lack of development of hair follicles. It may be apparent at or shortly after birth. Or, the cat may be born with a normal coat and then local or generalized hair loss occurs when the cat becomes a young adult.

In acquired hair loss, the cat is born with a normal hair coat. It has or had normal hair follicles at one time, and is or was capable of producing structurally normal hairs. Any disease that can affect hair follicles can cause hair loss. Disease may destroy the hair follicle or shaft or interfere with the growth of hair. Disease can cause the cat discomfort leading to self-trauma and loss of hair. Acquired hair loss can be inflammatory or noninflammatory.

Diseases that can directly cause destruction or damage to the hair shaft or follicle include bacterial, fungal, or parasitic infections; skin trauma such as burns; and (rarely) poisonings caused by mercury, thallium, or iodine. These diseases tend to be inflammatory.

Diseases that can inhibit or slow hair follicle growth include nutritional deficiencies (particularly protein deficiencies) or hormonal imbalances. Temporary hair loss can occur during pregnancy, while nursing, or several weeks after a severe illness or fever. These types of hair loss do not generally cause inflammation unless a secondary infection of the skin develops.

Itching or pain is a common cause of inflammatory hair loss. Diseases that commonly cause itching or pain include skin infections, parasites, and allergies. Friction may cause areas of hair loss, for example, poorly fitted halters or collars. Excessive grooming (usually caused by stress) can cause hair loss in some cats. Unlike dogs, many cats can hide their itching, and it may be hard to determine whether your cat is itchy.

Signs of hair loss may be obvious or subtle, depending on the disease. Congenital or hereditary hair loss is commonly either symmetric (appearing similar on both sides of the body) or localized to one region. It is usually not accompanied by inflammation. Signs of acquired hair loss are varied and often influenced by the underlying cause(s). Inflammation, color change, scaling, excessive shedding, and itching are common. Some causes may lead to the development of secondary skin diseases, such as infection or fluid discharge. Itching is variable, depending on the primary cause.

An accurate diagnosis of the cause of hair loss requires a detailed history and physical examination. The physical examination will cover both the cat's skin and its general health. The veterinarian will also look for signs of skin infections or parasites.

Shedding
Many cat owners seek veterinary assistance because their pet sheds excessively. You should remember that the natural development and growth of new hair is accompanied by the shedding of old hair. Shedding may be abnormal (excessive) if it results in obvious loss of the hair coat and bald spots. Abnormal shedding may be caused by bacterial infection. However, if the shedding is not accompanied by bald patches or symmetric hair loss, it is likely the shedding is just a stage in the natural replacement of the hair coat.

Your veterinarian may order laboratory tests in order to diagnose the cause of hair loss. These often include smears and culture of the skin to check for bacterial, fungal, or yeast infections. If these tests do not identify or suggest an underlying cause, a skin biopsy may be performed. If your veterinarian suspects a hormonal problem, he or she may order blood and urine tests.

Successful treatment depends on the underlying cause and specific diagnosis. Because identifying the underlying cause of the skin condition may take some time, many veterinarians will provide or prescribe medication to relieve any discomfort or itching your pet has in connection with the hair loss.

Last full review/revision July 2011 by Karen A. Moriello, DVM, DACVD; Thomas R. Klei, PhD; David Stiller, MS, PhD; Stephen D. White, DVM, DACVD; Michael W. Dryden, DVM, PhD; Carol S. Foil, DVM, MS, DACVD; Paul Gibbs, BVSc, PhD, FRCVS; John E. Lloyd, BS, PhD; Bernard Mignon, DVM, PhD, DEVPC; Wayne Rosenkrantz, DVM, DACVD; Patricia A. Talcott, MS, DVM, PhD, DABVT; Alice Villalobos, DVM, DPNAP; Patricia D. White, DVM, MS, DACVD