The hair follicle is a tube-like depression or pocket in the skin or scalp that contains the hair root. It is made up of a network of cells that produce the hair and a sebaceous gland that produces sebum, an oily substance that helps to keep the hair and skin healthy.
A hair follicle is a tube-like depression or pocket in the skin or scalp that houses the hair root. It is a complex, multi-layered structure composed of epidermal and dermal cells, which play crucial roles in hair growth, regeneration, and overall health. Key components of the hair follicle include:
- Hair bulb: The hair bulb is the swelling at the base of the hair follicle, which provides nourishment to the hair strand. It contains the dermal papilla, matrix cells, and melanocytes, all essential for hair growth and pigmentation.
- Outer root sheath: The outer root sheath is an extension of the epidermis that surrounds the hair follicle, providing support and protection. It also contains stem cells responsible for regenerating the hair follicle during the hair growth cycle.
- Inner root sheath: The inner root sheath is composed of three layers (Henle’s layer, Huxley’s layer, and the cuticle) and serves to guide and shape the growing hair strand as it emerges from the follicle.
- Hair shaft: The hair shaft is the visible part of the hair that extends from the skin’s surface. It is composed of keratinized, dead cells that have been pushed up from the matrix in the hair bulb.
- Sebaceous gland: The sebaceous gland is an oil-producing gland that is connected to the hair follicle. It secretes sebum, an oily substance that lubricates and protects the hair and scalp, keeping them moisturized and healthy.
- Arrector pili muscle: The arrector pili muscle is a small, involuntary muscle that attaches to the hair follicle. When it contracts, it causes the hair to stand up, creating the phenomenon known as “goosebumps.”
There are three main types of hair follicles: vellus, terminal, and transitional.
- Vellus hair follicles are small, thin follicles that produce short, fine hairs. They are found all over the body, except for the palms of the hands and soles of the feet.
- Terminal hair follicles are larger, thicker follicles that produce long, thick hairs. They are found on the scalp, face, and pubic area.
- Transitional hair follicles are in between vellus and terminal hair follicles. They are found on the scalp and face, and they can change from vellus to terminal hair follicles, or vice versa.
The hair follicle goes through three stages of growth: anagen, catagen, and telogen.
- Anagen is the growth stage. During this stage, the hair follicle is actively producing new hair. The anagen stage can last for two to seven years, depending on the location of the hair follicle.
- Catagen is the transitional stage. During this stage, the hair follicle stops producing new hair and begins to shrink. The catagen stage only lasts for a few weeks.
- Telogen is the resting stage. During this stage, the hair follicle is dormant. The telogen stage can last for several months.
After the telogen stage, the hair follicle enters the anagen stage and the cycle begins again.
Hair follicles are susceptible to a number of conditions, including:
- Alopecia is a condition that causes hair loss. There are many different types of alopecia, including male pattern baldness, female pattern baldness, and alopecia areata.
- Folliculitis is an infection of the hair follicle. Folliculitis can be caused by bacteria, viruses, or fungi.
- Hidradenitis suppurativa is a chronic skin condition that causes painful, swollen lumps under the skin. Hidradenitis suppurativa is most common in the armpits, groin, and under the breasts.