Also called canine flank alopecia, cyclic flank alopecia, and recurrent flank alopecia.

Dog with seasonal flank alopecia; Note the darkly pigmented skin in the areas of hair loss. Photo by MarVista Vet

What is Seasonal Flank Alopecia?

Seasonal flank alopecia is exactly what it sounds like, though it helps to know that the word alopecia means hair loss. With seasonal flank alopecia, a dog loses hair in the flank area on a seasonal basis. Different dogs seem to choose different seasons to lose their hair (fall and spring are popular), and when the season changes, the hair generally grows back. Sometimes a dog will skip a season only to lose hair again the next year. Most affected breeds are Boxers, Airedales, and English bulldogs, though numerous other breeds have been affected.

The hair loss is generally confined to the flanks (the area just ahead of the rear legs) though sometimes the bridge of the nose is involved. The skin is typically darkly pigmented in the areas of hair loss. Both flanks are generally affected symmetrically, and sometimes, there is a skin infection in the balding areas. Sometimes the hair re-grows in a different color than the original hair. Some dogs never re-grow their hair.

Diagnosis is generally made by the classic appearance of the pigmented bald spot and the history of recurrence. Diagnosis can be confirmed with skin biopsy if more confirmation is desired.

Why Does this Happen?

At the present time, no one knows why this occurs. It is felt to relate to the effects that the daylight cycle and light exposure have on the pineal gland. Shorter days seem to lead to a decrease in melatonin from the pineal gland, leading to skin change.

Breed predisposition suggests a genetic factor as well. Dogs of any age can be affected, but the average age is about four years.

Are There Treatment Options?

Melatonin, a natural biochemical that is important in regulating circadian (daily) rhythms, has been used successfully in many patients. In the U.S., this product is available as an oral dietary supplement or as an implant for use under the skin.   

Oral Therapy

Melatonin is sometimes used as a sleep aid in people, and the only known side effect is drowsiness. Dosing regimens must be obtained from the veterinarian treating your dog, but typically, oral melatonin is given 2-3 times daily. If the seasonal nature of the condition becomes predictable, it may be useful to begin the supplements a month or two before the hair loss is expected.

It is important to realize that nutritional supplements are not regulated in the same way that prescription drugs are. This means that the manufacturer of a nutritional supplement is not required to prove that the product actually contains the amount of active ingredient it claims to have. A study on melatonin products from the University of Tennessee found tremendous variability in content among different brands. The most consistent and accurate brand was found to be Nature's Bounty, so this is the brand that most dermatologists recommend.

Under Skin (Subcutaneous) Implant

A more effective method involves the use of melatonin implants under the skin. These were not available in the U.S. until recently. A small implant the size of a grain of rice is implanted under the skin and between the shoulders much in the same way as a microchip ID. If hair regrows and it seems to work, a new implant can be inserted every 4-6 months. Some drowsiness can be a side effect for the first one to three days, and occasionally a sterile abscess forms at the site, necessitating removal.

Seasonal flank alopecia is a cosmetic problem that is not harmful to the dog. It is not unreasonable to leave it untreated. Discuss these options with your veterinarian.