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Hair Follicles: Definition & Function

Hair Follicles: Definition & Function

Medical Director Dr. Hans-Georg Dauer

April 28, 2022

Our hair truly is a multi-talent. It protects us from heat on hot days and keeps us warm on cold days. And by the way, it also keeps foreign bodies out. Even mentally, the hair covering our head is valuable to us. What could give us more self-confidence and joy in life than a strong, healthy and shiny head of hair?

What a pity that we know so little about this supple and soft all-rounder on our head. It’s about time we changed that. Let’s take a close look at the hair follicle with all its strengths and weaknesses. Come on, let’s go.

What is a Hair Follicle?

The term hair follicle often makes us skeptical at first: What are these follicles? Never heard of them, huh?

Let’s take it from the top. The term follicle comes from Latin and is derived from folliculus. Translated, it means something like a vesicle. And this expression makes perfect sense. Because under the microscope, our hair looks like vesicular hollow structures, which we also call cell conglomerates.

This vesicle-shaped hollow structure on our head goes by many different names. There is the follicle, of course. But the experts sometimes also speak of folliculus pili. In German, by the way, we call the small, soft helpers Haarfollikel.

But where exactly do you find these follicles, folliculus pili or hair follicle? Quite simply, they are skin appendages in the dermis. To be more precise, the vesicle-shaped structures are always found around the hair roots. For a good reason: the follicles have to firmly enclose the roots in the dermis. Because this is the only way the hair anchors itself to the skin. Otherwise the hair doesn’t stay where it should.

Did you know that the hair follicles flow into our sebaceous glands? Exactly, because only through this connection, the gland can release its sebum undisturbed onto the skin’s surface. If it is prevented from doing so, it would become clogged.

The structure of a hair follicle is always the same: each hair follicle consists of an outer and an inner root sheath, which ensures a firm fit in the dermis.

Good to know: There are particularly many follicles on our scalp. No wonder, duh, this is where hair roots are found. And it is well known that follicles aren’t located far away from hair roots. It’s hard to imagine that there are around 100,000 to 150,000 hairs on our heads. We would never suspect that much hair just by looking at it, would we?

How are Hair Follicles Built?

A hair follicle always consists of two layers – the outer epithelial hair root sheath and the inner epithelial hair root sheath. Both tightly surround the human hair follicle and guarantee a solid fit in the dermis.

By the outer epithelial layer we generally mean a funnel-like invagination of the basal layer of our skin, in the so-called stratum basale. It forms a fine shell, you could say, for the hair root.

And then there is the inner epithelial hair root sheath. This directly surrounds the hair root. It is made up of three different layers:

  • inner layer (cuticle)
  • middle layer (huxley layer)
  • outer layer (henle layer)

Directly connected to the hair follicle are glands called sebaceous glands. As the name suggests, they are busy producing sebum. With good reason: did you know that sebum is a wonderful natural protective shield? It reliably protects our skin from germs and harmful substances.

Just below the sebaceous glands in the hair follicle, the so-called musculi arrectores pilorum are located. We are talking about tiny hair follicle muscles that can make our hair stand up. In other words, they are responsible for the well-known goose bumps.

In addition, there are fine nerve fibers that end in the hair follicle. They control the sympathetically innervated hair follicle muscles and benefit the sense of touch.

Hair Bulb

We can only see the outer part of our hair. That doesn’t mean there isn’t more to it than that. Right beneath the skin, the hair continues. We just can’t see it from our naked eyes.

This part hidden under the skin is called the hair root or radix pili. It is completely surrounded by epithelium, the top layer of human skin and mucous membrane. At the end of this particular section, it thickens into the hair bulb.

The bulb-shaped section of the hair in turn surrounds the so-called hair papilla. This is the physiological navigation center of the hair cycle. In other words, in the anagen phase (growth phase) it supplies the hair with precious nutrients and oxygen. At the same time, it drives natural hair growth through constant cell division. In the telophase (resting phase), these developments stop. The supply of nutrients and oxygen stops – just like cell division. The natural consequence: the hair withers and falls out.

Melagonesis by melanocytes also takes place in the hair bulb. And it is precisely this biochemical process that is responsible for the color of our hair.

The Medulla

Another central part of the hair is the medulla, the hair marrow. It is located directly inside of the hair. Here it provides the hair with stability and resistance.

Around the medulla grows the so-called fibrous layer, better known as the cortex. It tightly encloses the medulla and protects the pigments that determine our hair color.

This is followed by the outer, solid cuticle layer. This layer is a potent all-rounder: it reliably protects the hair from drying out, offers it support and also provides a silky shine – thanks to the many lipids.

What Tasks do the Hair Follicles Complete?

Whether on the scalp, in the beard or on our legs – hair follicles have the same tasks all over the body.

Task number one: The hair follicle carefully separates the surrounding connective tissue from the hair factory. This is because the hair factory must not be disturbed in its daily work. After all, it is responsible for the formation of new cells – an important duty for hair growth.

During the anagen phase, the growth phase of the hair, the hair factory diligently forms new cells. Step by step, the freshly formed cells join together to form the hair stem. Afterwards, it pushes the papilla of the hair bulb upwards over the hair root – until the hair shaft gradually emerges through the funnel-shaped invagination in the basal layer of our skin.

Fascinating fact: Hair follicles are formed as early as the sixth week of pregnancy – quite early, isn’t it?

Task number two: Our hair follicles cause goose bumps when we feel cold, scared, disgusted or excited. How? It’s simple: the hair follicle is connected to a very specific muscle – the musculus arrectores pilorum. As soon as this muscle is activated, it raises our hair.

Task number three: Our hair follicles are important for our sense of touch. Finally, the hair follicle is connected to countless fine nerve fibers that allow us to actively sense and experience our surroundings.

Task number four: Every hair follicle has a lubricating gland running through it. Its task: shortly before the newly formed hair shaft emerges from the skin, it greases it vigorously. In this way, it is optimally protected from heat, cold, chemicals and pollutants outside the body.

Task number five: Our hair follicles are involved in hair growth. They pave the way for blood vessels that carry precious nutrients and oxygen to the papilla. Because our hair can only ever grow at all if there are sufficient nutrients and oxygen – regardless of whether it is our head hair, our beard hair or our arm hair.

Task number six: A thriving metabolism in the hair follicles is also crucial for our hair color. After all, our hair follicle is also proven to participate in our body’s melanin production. And the more melanin we produce, the stronger and more vital our hair color is.

Hair Loss: What Causes it?

Oh no, not another bundle of hair on my pillow.

Hair loss is a shock. We are reluctant to say goodbye to the strong hair on our head. But don’t worry: to a point, hair loss is completely normal. We lose between 20 and 100 hairs daily.

Only after we’ve exceeded the 100 mark is it a raise for concern. Obviously, there is something more serious behind the hair loss, which, by the way, dermatologists refer to as effluvium. Yet what does it mean? What are the possible causes of alopecia?

Androgenetic Alopecia

Alopecia is an inherited condition. It is in our genes. In this case, we speak of hereditary hair loss or androgenetic alopecia.

Around 80 percent of all men and 40 percent of all women suffer from this visual flaw. Many people cope well with the change. Others are in constant despair. Women often find it difficult to come to terms with receding hairlines, thinning patches and a noticeably high forehead.

The reason for hair loss is a genetically determined hypersensitivity of the hair roots. They cannot tolerate DHT (dihydrotestosterone). If they come into contact with the male sex hormone, known as the hair loss hormone, they switch from the growth phase to the resting phase more quickly. And the faster the resting phase begins, the faster the hair falls out.

Did you know? In men, in the case of androgenetic alopecia, a crown usually forms on the top of the head. The hair at the back of the head remains the same. This is because they are immune to DHT.

Alopecia Areata

A less common form of hair loss is called alopecia areata. Its trademark: Circular, coin-sized bald patches form on the scalp. There is no specific pattern. The bald patches are randomly distributed all over the head.

The exact cause of the hair loss has not yet been clearly determined. However, experts suspect an autoimmune reaction of the body underlying the rare condition. The immune system turns against itself and destroys healthy hair cells. The consequence: the natural hair density decreases. The time it takes for new hair to grow back varies from patient to patient. For some it takes a few weeks, for others several months or even years.

Both men and women are affected. Overall, about one to two percent of the population suffers from alopecia areata.

Diffuse Hair Loss

Hair loss does not always have to follow a certain pattern, as in androgenetic alopecia or alopecia areata. It can also be entirely random. In this case, the expert speaks of diffuse hair loss.

Diffuse hair loss has a wide variety of triggers. From certain medications to hormonal fluctuations to iron deficiency, everything should be taken into consideration. Chronic stress or injuries and infections of the scalp may also be possible causes.

Most of the time, diffuse hair loss can be treated easily. As soon as the exact cause of the culprit is identified, it shouldn’t be too difficult to take the appropriate countermeasures.

In the case of stress, we prescribe relaxation. With yoga, meditation or long walks in nature, we calm our restless minds. In case of hormonal fluctuations, the dermatologist or gynecologist often prescribes hormones to compensate for the hormonal imbalance in the body. If the hair loss is the side effect of a medication, it is often advisable to change them out.

What is Hair and How is it Produced?

What is it that we actually carry around on our heads, legs or arms?

It’s quite simple: by hair we understand long threads of horn, i.e. threads of dead horn cells that grow out of the skin of all mammals – including humans.

Our entire body is hairy – except for the soles of our feet and the palms of our hands. Another exception is our mucous membranes and lips. They, too, always remain hairless. Hair is mainly consisting of keratin, water-insoluble fibrous proteins.

There are no blood vessels or nerves in our hair. They are simply attachments of our skin.

Hair serves an important function. Whether head hair or body hair – they all protect our skin, keep it warm and regulate the body’s temperature.

A Variety of Hair Types and Stages

  • Lanugo hair or wool hair: The delicate fluff covers the body of the fetus.
  • Vellus hair: These delicate, short hairs spread over the entire body – from arms and legs to hands and face. Unlike terminal hair, they have neither pigment nor hair marrow.
  • Terminal hair: The head, beard and body hair is called terminal hair. Both hair marrow and pigments are produced here. No wonder this type of hair is colored. The big difference to vellus hair: Terminal hair can grow long. In the case of scalp hair, it even takes three to six years to grow. In addition, the hair is hormonally sensitive. With a genetic predisposition, they can react hypersensitively to androgens and even fall out.

What is the Structure of a Hair?

Each individual hair is made up of two central components – a hair stem and a hair root. The visible part of the hair is the stem. It stretches out from the surface of the skin.

The hair root is the invisible part. It is hidden under the skin and extends into the subcutaneous tissue. Around the hair root are skin, connective tissue and the hair follicle, into which a sebaceous gland flows.

The cuticle provides the necessary protection of our hair. The outer cuticle provides stability, keeps the hair in shape and shields it from harmful influences such as heat and cold.

The Three Phases of Hair Growth

  • Growth phase (anagen phase): New hair is formed in the follicle in the scalp.
  • Transition phase (catagen phase): A radical change begins. Cell division stops, the supply of nutrients ceases.
  • Resting phase (telophase): The hair undergoes a process called “hornification” and falls out.