The hair follicle

Structure of the hair follicle

The hair follicle consists of several important components that work together to enable and support hair growth. Each part fulfills a specific function that is crucial for the health and stability of the hair.

• Hair bulb (bulbus pili): The “hair bulb”:/en/hairanatomy-hairgrowth-hairbulb.html is located at the very bottom of the follicle. This is where new hair cells are formed. It also contains the dermal papilla, which supplies the hair with important nutrients through a network of blood vessels.

• Hair root: The “hair root”:/en/hairanatomy-hairgrowth-hairroot.html is the part of the hair that is still in the skin, i.e., below the skin’s surface.

• Root sheaths: Layers that surround and protect the hair as it grows. There is an inner and an “outer root sheath”:/en/outer-root-sheath.html.

• Sebaceous gland: Produces oil (sebum) that keeps the hair soft and the skin supple.

• Hair erector muscle (“M. arrector pili”:/en/hair-muscle-musculus-arrector-pili.html): A small muscle that raises the hair (e.g., when cold or afraid – goose bumps).
• Hair follicle shaft: The “hair shaft”:/en/haarschaft.html is part of the follicle that extends upward to the skin surface.

Function of the hair follicle

The hair follicle performs a variety of tasks that are essential for hair growth and health. Not only does it ensure the formation of new hair cells, it also supplies the hair with nutrients, protects it, and reacts to external influences. The most important functions of the hair follicle are explained in more detail below.

• Enabling hair growth: New hair cells are constantly being produced in the hair follicle. These divide at the bottom of the hair bulb and push the hair upwards so that it grows out of the skin.
• Nutrient supply: The dermal papilla in the follicle supplies the hair cells with blood, i.e. with oxygen and important nutrients that support hair growth.
• Protection and shaping: The root sheaths (protective covers) surround the hair and ensure that it grows stably and in the correct shape.
• Production of sebum: The sebaceous glands in the hair follicle produce sebum, a fat that keeps the hair and skin supple and protects them from drying out.
• Reaction to the environment and hormones: The hair follicle reacts to hormones (such as testosterone) and external influences (e.g., cold, stress), thereby regulating hair growth.

• Sensory function: Nerves around the hair follicle enable the hair to perceive movement, e.g., when an insect runs over it.

  In short: The hair follicle is the “hair factory

Facts about hair follicles

• A person has about 5 million hair follicles all over their body.
• Of these, approximately 100,000 to 150,000 are on the scalp, which is where most of them are and where the hair on the head grows.
• Each hair follicle normally produces exactly one hair.
• Hair on the body (e.g., arms, legs) has much smaller or finer follicles than on the head.
• The number of hair follicles is roughly the same for everyone and is determined at birth.
• When hair follicles are damaged or destroyed, they usually cannot produce new hair.

Translated with DeepL.com (free version)

Common hair follicle disorders

The hair follicle can be affected by various disorders that disrupt hair growth or impair the health of the scalp. From hair loss to inflammation, the following common complaints show how diverse the problems affecting the hair follicle can be.

1. Alopecia (hair loss): Androgenetic alopecia is the most common form of hair loss, often referred to as “hereditary hair loss,” especially in men. In this condition, the hair follicles shrink due to the effect of certain hormones, known as androgens. As a result, they produce increasingly thinner hair until eventually no hair grows at all.

Alopecia areata is an autoimmune disease in which the immune system mistakenly attacks the hair follicles. This causes hair to fall out suddenly, usually in small, clearly defined, round patches.

Telogen effluvium describes sudden and diffuse hair loss triggered by stress, illness, or certain medications. Many hair follicles simultaneously enter the resting phase, leading to increased hair loss.

2. Folliculitis: Folliculitis is an inflammation of the hair follicles, usually caused by bacteria or fungi. This inflammation manifests itself as small, red pimples or pustules around the hair and may be accompanied by itching or pain.
3. Inflammation of the hair follicle (furuncle): This is a deep and painful inflammation of the hair follicle. Pus can form, which is why medical treatment is often necessary.

4. Fungal infections of the hair follicles (tinea capitis): These occur particularly frequently in children. They lead to scaly, bald patches on the scalp.

Hair follicles & laser hair removal

The hair follicle is the “root” of the hair, which sits deep in the skin and enables hair growth. Laser hair removal:/en/laser-hair-removal-berlin.html targets the hair follicle: The laser emits light that is absorbed by the melanin, the pigment in the hair. This light energy is converted into heat in the follicle, which destroys or damages the cells responsible for hair growth. As a result, hair grows back more slowly or stops growing altogether in the treated area.

Why not all hair disappears at once

Only hair follicles that are in the growth phase (anagen phase) respond well to laser treatment. Hair that is in the resting or transition phase is less responsive. Therefore, several treatments are necessary to catch as many hair follicles as possible in the right phase.