To understand why hair loss occurs, you first need to understand how the hair growth cycle works. This cycle consists of three phases: Anagen, Catagen and Telogen. Here we’ll look at the three stages of the hair growth cycle in detail and what can happen to cause hair loss.

Anagen: The Growth Phase

The Anagen phase is what 90 percent of your hair follicles are experiencing right now. As the growth phase of the hair growth cycle, Anagen can last for two to seven years. During this phase, the hair follicles push up hair at a rate of one centimeter a month or six inches a year.

Catagen: The Regressing Stage

The next phase of the hair growth cycle is Catagen, or the regressing phase. In this phase, hair follicles shrink to a fraction of their original length. The Catagen phase, lasting two to three weeks, cuts blood supply to the hair follicles, creating a club hair. Once the club hair appears it is a signal for the follicle to shed that hair.

Telogen: The Resting Phase

The final phase of the hair growth cycle is Telogen, or the resting phase. It affects 5 to 15 percent of your scalp’s follicles at any given time. Telogen lasts for 10 to 12 weeks, and up to 200 club hairs can be shed in a day. Telogen is the phase of the hair growth cycle where you may notice more hairs than usual on your pillow when you wake up in the morning.

What Happens During Hair Loss?

For most men and women hair loss is inherited. While outside factors can and do play a role in hair loss, 95 percent of men and 50 percent of women suffer from hair loss due to male pattern or female pattern baldness. In other instances, however, high levels of stress, hormonal changes or other medical conditions can stress the hair growth cycle, forcing your hair follicles into the resting stage prematurely. Sometimes these bodily changes can lead to temporary hair loss, such as what happens to women during pregnancy. Other times, however, the hair loss that occurs from these outside stressors is permanent.

Is Hair Loss Permanent?

Yes and no. Scientists now know the roots that give rise to our hair are alive and kicking just beneath the skin’s surface, even once the hair has stopped growing. There are drugs available that shorten the resting phase and force follicles into Anagen, allowing hair to grow back. There are other treatments for hair loss as well, but without some form of intervention, the hair will not grow back on its own.