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How Does Hair Grow: The Hair Growth Cycle Explained

Have you ever wondered how your hair grows? While it’s easy to take hair growth for granted, the reality is that the hair growth process is far more complicated than most people realize.

Hair growth occurs in a cycle, with your hair going through four distinct stages as it grows to its full length, regresses, rests and eventually sheds over the course of several years. 

Understanding hair growth is an important part of learning more about why your hair thins and falls out as you get older. 

It’s also useful knowledge for protecting your hair from the effects of male pattern baldness and regrowing your hair if you’re prone to hair loss.

Below, we’ve explained the entire hair growth cycle, from the early stages of your hair’s growth to what happens once each hair reaches its full length. 

We’ve also explained what you can do to combat and reverse the effects of hair loss from male pattern baldness using medication, lifestyle changes and other techniques.

The Four Hair Growth Stages

Like your skin, nails and other parts of your body, your hair constantly goes through a complex, multi-stage growth process. 

It’s important to understand that your hair is made up of two separate structures, each of which plays a role in its growth.

The first of these is the hair follicle, which lies under the surface of your scalp. Your hair follicles are living structures that produce new hairs through a complex process involving the creation of new cells.

The second structure is the hair shaft. This is the part of your hair that grows out from your skin. 

Each hair shaft grows from the hair bulb -- an area of the hair follicle that converts nutrients into the keratinized cells that make up your hair.

The hair growth process (or hair growth cycle, as it’s often referred to in medical literature) has three distinct stages:

  • The anagen (growth) phase. This is the active growing phase, during which your hair grows to its full length.
  • The catagen (regression) phase. This phase marks a transition of the hair from active growth into a resting phase.
  • The telogen (resting) phase. During this phase, your hair follicle becomes dormant and doesn’t actively grow.

Many hair growth experts also include a fourth phase in this process, which is referred to as the exogen, or shedding, phase. 

During this phase, the hair fiber detaches from the hair follicle, allowing a new hair to grow from the follicle in its place.

Each stage of the hair growth cycle lasts for a different amount of time, meaning your hairs may grow for years before entering the catagen, telogen and exogen phases.

Below, we’ve explained each hair growth phase in more detail to help you better understand the hair growth process.

The Anagen (Growing) Phase

During the anagen phase, your hair actively and continuously grows. About 85 to 90 percent of your hairs are in this stage at any one time.

All of the hair on your body goes through the anagen phase, although the duration of this phase can vary depending on the location of hair on your body.

On average, your scalp hair grows for between two and six years before reaching the end of the anagen phase. In comparison, the anagen phase for thigh hair is around two months.

This variation in the length of the anagen phase is the reason why the hair on your scalp is able to grow to a much longer length than the hair on your face and body.

The Catagen (Regression) Phase

After it passes through the anagen phase, each hair follicle enters the catagen phase. Referred to as the regression or transition phase, this period of the growth cycle involves the formation of a club hair -- a hair shaft that’s detached from the blood supply of the follicle.

During the catagen phase, your hair stops actively growing and the hair follicle, which previously supplied the hair with nutrients, shrinks slightly. This phase lasts for several weeks.

The Telogen (Resting) Phase

During the telogen phase, your hair follicle rests. The hair shaft also remains in a resting state, with no ongoing growth. 

Between 10 and 15 percent of the hairs on your scalp, face and body are in this phase at any given time.

Like the anagen phase, the telogen phase varies in length. Most body hair has a short telogen phase that only lasts for a few weeks, while scalp hair can go through a telogen phase of up to one year.

Certain health issues, such as stress, infections or illnesses that cause fever, may cause your hair to prematurely enter the telogen phase of its growth cycle, resulting in a form of hair loss that’s referred to as telogen effluvium.

This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.