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What is a Hair Follicle?

Niki Acker
By
Updated Mar 03, 2024
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The hair follicle is a structure of the skin from which hair grows. There are hair follicles all over the skin, with the exception of the lips, palms of the hands, and soles of the feet. Hair follicles grow hair by packing old cells together.

The hair follicle is supplied with one or more sebaceous glands, which provide sebum, an oily substance that helps lubricate the hair and skin. Apocrine sweat glands also help lubricate the hair follicles of the armpits, groin, and areolae. Areas that have thicker hair growth, such as the scalp, have more sebaceous glands. In addition the the sebaceous gland, the hair follicle is provided with the arrector pili, a bundle of muscle fibers that creates goose bumps when contracted. Hair follicles also have stem cells at their base, which contribute to regular hair growth.

The base of the hair follicle is called the papilla. It consists of connective tissue and a capillary loop, or tiny blood vessel. The papilla is surrounded by the hair matrix, which consists of epithelial cells and melanocytes. The epithelial cells divide very quickly, causing regular hair growth, while the melanocytes provide pigment, and are responsible for hair color.

The hair follicle is surrounded by a protective root sheath, consisting of the external and internal root sheath. The internal root sheath, in turn, has three layers: the innermost internal cuticle, the medial Huxley's layer, and the outermost Henle's layer. The internal cuticle is continuous with the outermost layer of the hair fiber. The hair fiber also has three layers: the cuticle, the intermediate cortex, and the inner medulla.

Hair growth takes place in four-phase cycles. Anagen is the active growth phase, the length of which varies greatly between people and individual hair follicles. Anagen lasts for two to seven years on the human scalp, but for only months on the eyebrows. The growth phase is followed by catagen, a brief transition phase lasting for approximately two to four weeks.

After catagen, the telogen phase, a resting phase, begins. Hairs in the telogen phase are dead and are called club hairs. Many club hairs are shed from the body daily. The telogen phase lasts about three weeks for hairs on the human scalp. The final stage of the hair follicle cycle is exogen, a shedding phase in which one of many hairs that may arise from a single follicle is shed.

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Niki Acker
By Niki Acker
"In addition to her role as a The Health Board editor, Niki Foster is passionate about educating herself on a wide range of interesting and unusual topics to gather ideas for her own articles. A graduate of UCLA with a double major in Linguistics and Anthropology, Niki's diverse academic background and curiosity make her well-suited to create engaging content for WiseGeekreaders. "
Discussion Comments
By Perdido — On May 17, 2012

@shell4life – I've had that same issue, and I believe it is called folliculitis. My underarms would break out in painful raised bumps with white heads after I shaved them, and I found a couple of ways to help prevent this.

First, I quit using deodorant right after getting out of the shower. It seemed to be irritating my armpits, so I switched to applying aloe vera as soon as I dried off. This felt so soothing, and it never caused a problem for my hair follicles.

Next, I switched to shaving them every other day instead of every day. This gave my follicles a chance to recover, and they started looking so much better.

By shell4life — On May 17, 2012

I have had inflamed follicles after shaving my bikini line, and it was very uncomfortable. I looked as if I had some hair follicle disease, because I had a row of bright red bumps filled with white pus.

It seemed that this happened to some degree every time that I used a disposable razor. I would put aloe vera gel on the bumps to ease the itching and pain, but I would just have to wait several days for them to go away.

I finally got an electric razor, and I haven't had the inflamed follicles since I started using it. Electric razors are much gentler on the skin, and I use mine on sensitive areas prone to breakouts.

By cloudel — On May 16, 2012

I didn't know that hair could only grow for seven years. That's very interesting.

Maybe that explains why some people just cannot seem to grow their hair very long. They probably just have genetically slow hair growth, and by the time their hairs are seven years old, they just didn't make it very far.

Other people can grow more than six inches of hair a year, so they could potentially wind up with hair far below their waists. I am one of these people, but I always cut my hair before it gets past my waist, because it gets really inconvenient.

By ddljohn — On May 15, 2012

@turquoise-- Yea, my company had it done for all their employees one time.

They took a hair sample close to the scalp and sent it to the lab for testing. I believe they test for marijuana, cocaine, opiates and the like. I don't think they would test for prescription drugs. But you can find out by speaking to the insurance company.

The hair follicle test for drugs is a good test because it's pretty effective and accurate. When drugs are used the drug metabolites enter the hair follicles through the bloodstream and settle into the hair as it grows. Since it takes some time for hair to grow, it doesn't show drugs that are used really recently (a couple of weeks). But it does show drugs that were used in the past 3 months before that.

By turquoise — On May 14, 2012

I have to take a hair follicle drug test in a couple of weeks for a job I've applied for. I've never heard of this test before. Has anyone here gone through with it?

What is it like, how does it work and what kind of substances do they test for?

The only thing I'm on is prescription anti-depressives. I'm wondering if that will show up in the test? I'm a little worried that this might affect their opinion for the hiring process.

If anyone has any knowledge about the hair follicle test, please let me know!

By fify — On May 14, 2012

Oh so shedding hair periodically is normal?

I had no idea that the hair follicle works in phases like this. I thought that the hair just continuously grows and that shedding is a bad thing.

I've been shedding a lot of hair these past couple of days so I guess my hair follicles are either in the telogen or exogen phase.

I'm not going to heed all these advertisements on TV for hair products that prevent hair shedding anymore. Clearly, they're not telling us enough about how our hair follicles work for monetary gain.

Niki Acker
Niki Acker
"In addition to her role as a The Health Board editor, Niki Foster is passionate about educating herself on a wide range...
Learn more
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