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Is he scratching it out or is it falling out?

Is the hair falling out from infection or demodicosis?

Are the hair follicles no longer cycling?

What conditions are associated with the hair cycle abnormalities?

What is Alopecia X?

How is Alopecia X diagnosed?

How do we treat Alopecia X?

What do we know about the hair cycle in dogs?

Dr. Linda A. Frank
Department of Small Animal Clinical Sciences
College of Veterinary Medicine
The University of Tennessee
Knoxville, TN 37996-4544
Tel: (865) 974-8387 (ET) Email:



What do we know about the hair cycle in dogs?

It is amazing how little is known about the hair cycle in general. Most of the research has concentrated on male pattern baldness in people. The actual factors that control the hair cycle are not precisely known and are under active investigation. There are many factors that influence the hair cycle; however, no regulator molecules have been identified that are specific for the hair. In other words, the factors not only affect hair but have other effects within the body.

What we do know is that the hair cycle consists of an active growth phase, termed anagen, in which the hair reaches its genetically determined length. It then passes through a transient catagen phase as it proceeds to enter the resting phase termed telogen. In people the hair follicle spends most of the time in anagen. This phase can last years, depending on the ultimate length of your hair as determined by your genes. Once the hair enters the resting (telogen) phase, a new anagen hair starts growing and the telogen hair is shed. This predominantly anagen cycle that is seen in people is probably similar to the hair cycle of dogs that need regular hair cuts, like poodles.

The rest of the dogs have, what has been termed, a telogen-predominant cycle. The anagen phase is short, long enough to achieve the genetically desired length of coat. Therefore, the anagen phase lasts probably anywhere from one month to a year or more. The hair then cycles into telogen and remains there for a prolonged period of time. This hair is tightly bound within the follicle and will not readily fall out or be pulled out. In the Nordic breeds, it is thought that the telogen phase may last for years. Replacing an entire dense coat yearly is very energy-dependent. At some point the telogen hair falls out and is replaced by a newly developing anagen hair; thus the cycle continues. The trigger for the telogen hair to fall out and a new hair to grow is not known at this time.

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