Medically reviewed by Katelyn Hagerty, FNP
Written by Our Editorial Team
Last updated 5/18/2021
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.
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.
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.
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.
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.
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As new hair starts to grow from the hair follicle, the old hair enters into the exogen phase, or shedding phase.
During this phase, the hair fiber detaches from your scalp and falls out. It’s normal to shed about 50 to 100 hairs every day through this process.
You may notice these hairs on your pillowcase, in your hairbrush or stuck inside your shower drain.
Since each hair is replaced by a new one growing from the same follicle, the hair shedding that occurs in the exogen phase doesn’t contribute to male pattern baldness.
Just like other important processes in your body, the hair growth process can be interrupted and affected by extrinsic factors like stress, malnutrition, and illness.
For example, early hair shedding often occurs as a result of nutritional deficiencies, rapid weight loss, excessive amounts of stress and illnesses or injuries.
When your hair growth cycle is interrupted, it often takes several months before you’ll be able to notice any difference in your hair.
This is because your hair needs to go through the telogen phase of the hair growth cycle before shedding.
Since the telogen phase can last for several months, hair shedding often starts a few months after the triggering event.
For example, if you go through an illness that gives you a fever (a common cause of hair growth cycle interruption and telogen effluvium), you may not experience any hair shedding until one to six months after the causative event.
Simple habits can help you to promote healthy hair growth and avoid shedding throughout your hair’s growth cycle. Try to:
Countless vitamins and minerals, including vitamins A, B7, B12 and essential nutrients such as zinc and iron, all play key roles in your body’s process for growing and maintaining your hair.
Try to eat a balanced, nutritious diet that’s built around fruits, vegetables, whole grains and lean, healthy sources of protein.
Telogen effluvium, a common cause of hair shedding, is often linked to chronic health issues such as hypothyroidism, iron deficiency or sudden changes in your production of important hormones.
Many of these issues can be detected through routine blood testing, making it important to get yourself checked regularly by your primary healthcare provider.
Stress is a common cause of telogen effluvium. It’s also a major risk factor for issues such as high blood pressure, depression and certain forms of anxiety.
If you’re feeling stressed, try techniques like deep breathing and meditation to promote relaxation. Making changes to your habits, lifestyle and working environment may also help to reduce your stress levels.If
Almost everyone is aware of the negative effects smoking can have on your cardiovascular health and risk of developing lung cancer. Fewer people are aware that smoking can also damage your hair and contribute to hair loss.
Research shows that the toxins in cigarette smoke can reduce blood flow in your scalp and damage the DNA of your hair follicles.
If you smoke, try to quit. Our guide to quitting smoking lists techniques that you can use to manage your cravings, avoid smoking triggers and stay smoke-free for the future.
Our guide to natural changes for improved hair growth shares other simple techniques that you can use to promote healthy hair growth.
Male pattern baldness is the most common form of hair loss in men. Unlike telogen effluvium, which is temporary, hair loss due to male pattern baldness tends to be permanent.
This form of hair loss is caused by a combination of your genes and the effects of the hormone dihydrotestosterone, or DHT.
Over time, DHT can bind to receptors in your scalp and cause your hair follicles to go through a process called miniaturization.
During this process, your hair follicles shrink and eventually stop producing new hairs.
Some research suggests that DHT stimulates TGF-β1, TGF-β2, DKK1 and interleukin 6, which are proteins that play a role in your hair growth cycle.
Not all of your hair follicles are sensitive to DHT. Most of the time, male pattern baldness affects the follicles around your hairline and crown, without any effect on the hair at the back and sides of your scalp.
Since hair loss can occur for several reasons, there’s no one-size-fits-all method for regrowing hair. Instead, the most effective way to regrow your hair depends on how you lost it.
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 licensed healthcare provider and learn more about the solutions that are available to you.
If your hair loss is caused by a nutritional deficiency, making changes to your diet may help to restart your hair growth cycle and promote regrowth.
If you’re experiencing the early symptoms of male pattern baldness, such as a receding hairline or hair loss around your crown, your best bet is to treat it with medication.
It’s available with a prescription and works by stopping your body from producing the hormone that causes baldness to develop.
The second is minoxidil -- a topical, over-the-counter medication that works by encouraging your hairs to enter into the anagen phase of the growth cycle.
Minoxidil may also help to stimulate blood flow in your scalp to provide your hair follicles with the nutrients they need to produce strong, healthy hair.
It’s important to understand that you can only regrow hair in the areas of your scalp with healthy, active hair follicles.
If you’ve lost hair in a specific part of your scalp for several years, such as a receding hairline, it may not grow back even with daily finasteride and minoxidil use.
There’s also no guarantee that the hair you’ve lost due to male pattern baldness will grow back, even in areas where it’s only recently started to thin.
It’s best to think of hair regrowth as a bonus, not as a predictable effect of using finasteride and minoxidil.
The better you understand the hair growth process, the easier it is to tell the difference between regular hair shedding and male pattern baldness.
This understanding can help you to identify the signs of male pattern baldness and take action quickly to protect and keep your hair.
It can also save you a lot of stress if you notice shedding but recognize that it’s just the natural result of your hair follicles entering into the final phase of the growth cycle.
If you’re starting to lose your hair and want to take action, you can view our full range of proven, science-based hair loss medications online.
You can also find out more about the common signs of hair loss, risk factors and treatments in our detailed guide to male pattern baldness.