Hair Shedding and the "Exogen" Phase

Exogen Phase

There are various phases of the hair growth cycle that you may have heard of such as anagen, catagen and telogen. Anagen is the growing phase. Catagen is the transitional phase. Telogen is the resting phase where hairs stop growing. At the end of the telogen phase, hairs shed from the body- and end up in our brushes, combs, and shower drains.

So what is the "exogen phase"? Well, for years it was thought that once a hair is ready to be shed, it simply leaves that scalp when a hair underneath pushes it out. We know now that is untrue. A hair can of course leave the scalp when enough tug is given to it. However, the departure of a hair from the scalp is now recognized to be a highly regulated process which is known as "exogen." Therefore, hairs are not simply pushed out of the scalp - the process is tightly regulated.

This picture shows the scalp of a patient with a telogen effluvium (hair shedding disorder). Upright regrowing hairs (URG) are seen. In addition, a telogen hair (also called a club hair) can also be seen. This hair has officially been shed from the patient's scalp. It is nested amongst the existing hair. At the time of the next patient's next shampooing or brushing it will likely be removed completely from the scalp.