Merck Manual

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Pet Owner Version

Hair Loss (Alopecia) in Cats


Karen A. Moriello

, DVM, DACVD, Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison

Reviewed/Revised Aug 2018 | Modified Oct 2022
Topic Resources

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 Hereditary Hair Loss (Alopecia) Cats can be born with or may inherit several different kinds of skin abnormalities. Some inherited skin disorders can become visible weeks to months after birth. Most of these conditions are... read more 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 (for example, pain or itchiness) leading to self-trauma and loss of hair. Acquired hair loss can be inflammatory or noninflammatory (such as is seen with hormonal disorders). Inflammatory disorders are the most common cause of alopecia.

Diseases that can directly cause destruction or damage to the hair shaft or follicle include bacterial, fungal, or parasitic infections; severe inflammatory diseases (such as deep skin infections); skin trauma (such as burns or radiation); 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. Significant hair loss is common in cats after respiratory infections. 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 bacterial or fungal skin infections, parasites, and allergies. Less commonly, skin tumors can cause hair loss. 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.

Feline acquired symmetric alopecia (formerly called feline endocrine alopecia) is a syndrome that describes hair loss on both side of a cat's body that occurs due to an underlying disease. The most common cause is flea allergy dermatitis Flea Allergy Dermatitis Fleas are small, wingless insects that feed on animal blood. Besides being a nuisance, they can also transmit diseases and cause allergies or anemia. There are more than 2,200 species of fleas... read more Flea Allergy Dermatitis . In cats that do not have an obvious flea infestation, your veterinarian may perform blood tests. Your veterinarian may also recommend a trial of flea control treatments to see if improvement is seen.

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, skin color change, scaling, thickening or redness of the skin, 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. Alopecia caused by hormonal disorders is not usually itchy at first, unless there is a secondary skin infection.

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.


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. Flea combing and skin scrapes may also be performed to look for parasites. 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.

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