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Hair Follicle Function: What Exactly is a Hair Follicle?

Mary Lucas, RN

Medically reviewed by Mary Lucas, RN

Written by Our Editorial Team

Last updated 5/15/2022

If you’re starting to develop the early signs of male pattern baldness, or if you’re simply curious about how your hair grows, you might have wondered what your hair follicles are and how they function. 

Your hair follicles are tiny but complex structures located inside your skin. Not only do they play a critical role in the growth of your hair, but they also contain glands that produce and release a type of natural oil called sebum.

Healthy hair follicles are essential not just for a full head of hair, but also for smooth and healthy skin.

Below, we’ve explained what hair follicles are, as well as how they function to produce hair and regulate certain aspects of your skin health. We’ve also discussed how conditions such as male pattern baldness can affect your hair follicle function and cause noticeable hair loss. 

What Is a Hair Follicle?

A hair follicle is a tiny structure, sometimes referred to as a “mini-organ” that’s found within your skin. Each follicle starts as a small opening in your epidermis — a tiny but visible hole in the skin that’s often referred to as a pore.

Hair follicles usually extend into the dermis and subcutis, which are the inner layers of your skin.

Although a hair strand might look simple from the surface of your skin, it’s actually a complicated structure that contains a follicle and hair root, an oil-producing sebaceous gland, and a small but important muscle called the arrector pili, or hair erector.

These different parts of each hair follicle work together to facilitate hair growth, give your skin its protective function, stimulate nerve endings and act as a sensitive touch receptor, and generate heat when your body becomes cold.

Put simply, although hair follicles are best known for their ability to produce hair, there’s far more than just one hair follicle function. 

How Hair Follicles and Hair Growth Work

Before we get into the secondary functions of your hair follicles, let’s discuss the most significant one: producing hair.

Hair follicles are found all over your body, from your scalp and face to your armpits, genitals and buttocks, and even the insides of your nose and ears. Even areas without any visible hairs, such as your earlobes and forehead, also contain hair follicles.

Each of these hair follicles can create hair, with the average length, thickness and visibility of the hair varying based on the type of follicle and a process referred to as the hair growth cycle. 

The Hair Growth Cycle 

Every hair on your body, from your scalp to your legs, grows as part of a complex process that’s known as the hair growth cycle. 

This process involves multiple phases, during which a hair shaft (the visible part of your hair that you can see and touch) grows out from the hair bulb inside the hair follicle. As the hair grows to its full length, it eventually rests before shedding and being replaced by a new h\air.

The first phase in the hair growth cycle is the anagen phase, or growth phase. In this phase, the hair follicle actively produces a new hair shaft. Epithelial stem cells stimulate the growth of hair downwards, creating a hair bulb, which then grows upwards and breaks through the skin.

The anagen phase can vary in length depending on the location of hair on your body. Scalp hair follicles typically spend two to six years in the anagen phase, while hair follicles in other areas of your body may only spend a few months in this phase.

The second phase in the hair growth cycle is the catagen phase, or transition phase. During the catagen transition, cell division inside the hair matrix stops, and your hair transitions from active growth to regression. The hair forms into a “club hair,” with a small white node at its end. 

The third phase in the hair growth cycle is the telogen phase, or resting phase. Hairs that are in the telogen phase no longer actively grow, but remain attached to the scalp for around 100 days before shedding.

This shedding period is referred to by some experts as the “exogen” phase and is viewed as its own distinct phase in the hair growth cycle.

At any given time, between 85 and 95 percent of your hair follicles will typically be in the anagen phase of the hair growth cycle. This cycle allows your hair to continuously grow, with new hairs replacing old ones as they shed and re-enter the cycle.

Our full guide to the hair growth cycle provides more information about how your hair grows and sheds, as well as the impact that the growth cycle can have on your hair’s thickness and overall appearance. 

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Hair Follicles and Sebum Production

Through the attached sebaceous gland, each hair follicle in your skin also plays a key role in the production of sebum. 

Sebum is a type of natural oil that’s secreted by your sebaceous glands. It’s critical for your skin health and function. In fact, the sebum produced by your sebaceous glands accounts for around 90 percent of the lipids that lubricate and protect your skin surface.

Sebum is produced inside a sebaceous gland. It then empties in the follicular canal, from which it travels to the surface layer of your skin via a wicking action. This is one reason why you may notice that your skin tends to feel oily in the areas of your body with lots of hair. 

As sebum moves from your hair follicles to your skin’s surface it provides a variety of important functions, including lubricating your skin and creating a physical barrier that provides protection against bacteria, fungi and other potential sources of infection.

Unfortunately, sebum can also cause certain problems. For example, when too much sebum is released from your sebaceous glands, it can mix with dead skin cells and produce sebum plugs in your hair follicles, resulting in whiteheads, blackheads and other types of acne.

Hair Follicles and Heat

Your hair follicles aren’t just used to grow hairs and produce sebum — they also play a vital role in keeping your body warm.

A small muscle called the arrector pili can be found at the base of each of your hair follicles. If your body temperature starts to drop, these muscles all contract at the same time in order to produce heat throughout your skin tissue.

This muscle contraction is what causes your hair to “stand up straight” when you spend time in a cold environment.

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Hair Follicles and Male Pattern Baldness

Male pattern baldness, also referred to as androgenetic alopecia, is the most common form of hair loss in men. It’s the type of hair loss that’s responsible for classic signs of balding, such as a receding hairline or bald spot around your crown.

This type of hair loss occurs when your hair follicles are damaged by a hormone called DHT, or dihydrotestosterone. 

Over time, DHT  can activate hormone receptors in your scalp and cause your hair follicles to go through a process called miniaturization. This process shortens the anagen phase of your hair growth cycle, leading to smaller, thinner hair follicles.

Unlike healthy hair follicles, miniaturized hair follicles aren’t capable of producing viable hairs. In some cases, the hairs produced by affected follicles may not even penetrate through your scalp, resulting in visible hair loss. 

For the most part, male pattern baldness is a genetic issue. Research suggests that people with this type of hair loss have above-average levels of DHT, as well as greater levels of sensitivity to the effects of DHT in the scalp.

Male pattern baldness is treatable with medications such as finasteride and minoxidil, as well as through procedures such as hair transplant surgery

We offer several FDA-approved hair loss medications online, with finasteride available following a consultation with a healthcare provider who will determine if a prescription is appropriate. 

You can also learn more about how these medications and procedures work in our full guide to what you should take for hair loss

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Learn More About Improving Your Hair Health

Your hair follicles play an essential role in producing thick, healthy hair. They’re also involved in maintaining your skin’s ability to function as a protective barrier, and even keeping you warm as the temperature drops.

Because of this, proper hair follicle function is vital for maintaining your hair and stopping issues such as male pattern baldness. 

If you’re interested in improving your hair follicle and hair root function, you can learn simple but effective techniques in our guide to healthy hair habits for men

You can also learn more about dealing with male pattern baldness and other types of hair loss in our guide to the best treatments for thinning hair.

8 Sources

Hims & Hers has strict sourcing guidelines to ensure our content is accurate and current. We rely on peer-reviewed studies, academic research institutions, and medical associations. We strive to use primary sources and refrain from using tertiary references.

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  2. Hair follicle anatomy. (2021, April 14). Retrieved from https://medlineplus.gov/ency/imagepages/9703.htm
  3. Acne. (n.d.). Retrieved from https://www.americanskin.org/resource/acne.php
  4. Hoover, E., Aslam, S. & Krishnamurthy, K. (2021, October 14). Physiology, Sebaceous Glands. StatPearls. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK499819/
  5. Skin Anatomy. (n.d.). Retrieved from https://www.hopkinsmedicine.org/neurology_neurosurgery/centers_clinics/cutaneous_nerve_lab/patients/skin_anatomy.html
  6. Ho, C.H., Sood, T. & Zito, P.M. (2021, November 15). Androgenetic Alopecia. StatPearls. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK430924/
  7. Schneider MR, Schmidt-Ullrich R, Paus R. The hair follicle as a dynamic miniorgan. Curr Biol. 2009 Feb 10;19(3):R132-42. Available from: https://pubmed.ncbi.nlm.nih.gov/19211055/
  8. Milner Y, Sudnik J, Filippi M, Kizoulis M, Kashgarian M, Stenn K. Exogen, shedding phase of the hair growth cycle: characterization of a mouse model. J Invest Dermatol. 2002 Sep;119(3):639-44. doi: 10.1046/j.1523-1747.2002.01842.x. Erratum in: J Invest Dermatol. 2003 Jun;120(6):1138-9. Available from: https://pubmed.ncbi.nlm.nih.gov/12230507/

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. Learn more about our editorial standards here.