Dog: Seasonal Hair Loss

General information

Other common/scientific names: Cyclic Alopecia, Cicatrical Alopecia

Seasonal hair loss or alopecia is a condition that occurs during certain seasons, usually the colder months. The hair follicle is a cavity in the skin that produces hair. Dogs have compound hair follicles where the primary hair and secondary hairs emerge through the same pore. Hair loss occurs when hair formation in the follicle is disrupted.

Abb. GGKJHYF7: This is an illustration of the structures of the skin including the hair follicles.


The cause of seasonal hair loss is not completely understood. One theory suggests that the hair loss is caused by the lack of sunlight exposure to the pineal gland. This is due to the shortened daylight hours during the winter months. While it is unclear why this causes hair loss, the hormone, melatonin (produced by the pineal gland) may play a role. Boxers, English bulldogs and Airedale terriers are more commonly affected.

Cardinal symptom

Symmetrical hair loss


The hair loss is bilaterally symmetrical which means both sides of the dog are affected evenly. The hair loss begins in the flank and can involve the haircoat on the back of the dog. This condition is not pruritic (itchy) and there is no dermal inflammation; however, the skin may become hyperpigmented.


Diagnosis of seasonal hair loss can be made from the history, breed and physical examination. A skin biopsy can be performed to rule out other skin diseases.


Treatment is not necessary in most cases since the haircoat will re-grow within 3-5 months when the season changes. For recurring cases or cases where the hair does not re-grow, oral melatonin has been used. Increasing a dog’s exposure to sunlight may also be beneficial.


The prognosis is good for seasonal hair loss.


Injectable melatonin has been used to prevent seasonal hair loss. This product is not available in the U.S.

Update version: 4/24/2014, © Copyright by
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