Everything You Need to Know About the Hair Growth Process & Regrowing Hair

There’s far more to hair growth than many people realize. The hair growth process occurs in a cycle, with hair follicles going through four different stages as they grow, regress, rest and shed over the course of several years.

Understanding hair growth is an important part of learning more about why your hair thins and falls out. It’s also useful knowledge for regrowing your hair and helping you maintain as much hair as possible over time.

In this guide, we’ll explain the entire hair growth process, from the growing phase right through to shedding and regrowing hair. We’ll also explain how understanding the hair growth process can help you combat and reverse the effects of hair loss.

The Four Stages of Hair Growth

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

• The anagen, or growing phase, during which your hair grows.
• The catagen, or regression phase, during which your hair follicles shrink and detach from your skin.
• The telogen, or resting phase, during which new hair begins to grow under the older, detached hairs.
• The exogen, or shedding phase, during which the older hair falls out from your scalp and is replaced by the new hair.

Each of these stages lasts for a different amount of time, meaning your hair can grow for years before it enters into 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 is actively and continuously growing. This phase of the hair growth process usually lasts for three to five years, although some people have anagen phases of up to seven years.

Because your hair is continuously growing during the anagen phase, the length of this phase of the hair growth cycle determines the maximum length of your hair. For most people, this is 18 to 30 inches.

The Catagen (Regression/Transition) Phase

After each hair follicle completes its anagen phase, it enters the catagen, or regression phase. A hair follicle in the catagen phase will shrink slightly in size and detach from your skin, starting its process of falling out.

Although hair in this phase "detaches" from your skin, it usually doesn’t fall out until much later, usually when the new hair “pushes” it out from your scalp.

The Telogen (Resting) Phase

After a hair follicle enters the catagen phase and detaches from your scalp, it enters a resting period known as the telogen phase. This phase usually lasts for three to five months before a hair is "pushed" out by the growth of new hair.

Most people have about 10 to 20% of their hair in the telogen phase at any time. Sometimes, when a person is stressed or physically unwell, other health conditions can cause more hair follicles than normal to enter the telogen phase, resulting in temporary hair shedding.

The Exogen (Shedding) Phase

Once the new hair has grown, the old hair enters the exogen phase. During this phase, the old hair completely detaches from the scalp and falls out, usually while you’re using a comb, brush or washing your hair in the shower.

It’s normal for about 50 to 150 hairs to go into this phase and fall out on a daily basis, meaning there’s no need to panic if you notice a few hairs on your comb or brush after styling your hair.

As the new hair grows, it replaces the old hair and completes the hair growth cycle, giving you replacement hairs for all of the hairs lost during the catagen, telogen and exogen phases of the growth process.

Understanding the Hair Growth Process

Just like other important processes in your body, the hair growth process can be interrupted and affected by external factors like stress, malnutrition, and illness.

For example, a lack of protein can cause hair to enter the telogen phase prematurely, resulting in excessive thinning and hair loss. Animal studies also show that stress can inhibit hair growth by causing hair to enter into the catagen phase prematurely.

Because the process of shedding hair takes several months (remember, the telogen phase is a three to five month process for most people), changes in your diet or stress levels can result in hair loss that doesn’t happen until months later when your hair enters into the exogen phase.

This means that if you suddenly start feeling stressed or stop getting enough vitamins or minerals, it could take months to notice a difference in your hair.

As always, the best way to prevent this type of damage to your hair is to eat a healthy diet and consume the most important vitamins and minerals for healthy, thick and strong hair.

Male Pattern Baldness and the Hair Growth Process

Male pattern baldness affects the hair growth process by making the effects of the catagen, or regressive, phase more severe.

DHT, the androgenic hormone that causes male pattern baldness, stimulates TGF-β1, TGF-β2, DKK1 and Interleukin 6, all of which have an effect on the miniaturization of hair follicles. Over time, this results in hair follicles shrinking and eventually failing to produce hair growth.

Not all hair follicles are sensitive to the effects of DHT. Most of the time, the miniaturization part of the hair growth process affects hair follicles around the hairline or crown first, before starting to affect other hair follicles that are sensitive to DHT.

How to Regrow Hair

There are several ways to regrow hair. The most effective way to regrow your hair depends on how you lost it, whether the root cause is your diet, stress levels or androgens.

If your hair loss is caused by stress, the best way to reverse the effects and regrow your hair is to remove the source of stress from your life. For severe stress, it’s always a good idea to speak to a doctor and learn more about the best solutions.

If your hair loss is caused by a nutritional deficiency, the best way to regrow your hair is to make changes to your diet and supplementation regimen. Again, it’s always a good idea to speak to a doctor for an expert opinion.

If your hair loss is the result of male pattern baldness, the best way to start regrowing some of the hair you’ve lost is by blocking dihydrotestosterone (or DHT), which is the root cause of male pattern baldness.

You can also use topical sprays and gel products such as minoxidil, which shortens the telogen phase and causes old hairs to shed and be replaced by fresh, new hairs in the anagen phase.

It’s important to know that you can only regrow from areas where the hair follicles are still active, healthy and capable of producing new hairs. If you’ve lost hair in an area for several years, there isn’t much chance of it regrowing even with a full dose of finasteride and daily minoxidil usage.

There’s also no guarantee that any of the hair you’ve lost as a result of male pattern baldness will regrow, even in areas where it’s only recently started to thin. It’s best to think of regrowth as a bonus, not as a predictable effect of using finasteride and minoxidil.

Understanding Hair Growth

The better you understand the hair growth process, the easier it is to tell the difference between regular exogen shedding and hair loss.

This can help you take action sooner if you notice your hair starting to thin. It can also save you a lot of stress if you notice shedding but recognize that it’s just the natural result of your follicles entering into the final phase of the growth cycle.

For the most part, it’s best not to panic about your hair’s growth rate or male hair loss. Instead, take a reasoned approach to your hair and approach hair loss as a choice by taking action to limit your future hair loss and retain as much of your hair as possible.

This article was reviewed by Brendan Levy, MD.