Structure of Hair

The hair root is located beneath the scalp, within the hair follicle, and is composed of living cells.
The hair shaft is located above the scalp and is composed of keratinized cells.
The outer layer of the hair shaft is the cuticle, the middle layer is the cortex, and the inner layer is the medulla.

Hair Growth

Newly formed hair follicles are closer to the surface of the skin, making them relatively fragile and prone to breakage.
As hair grows, the follicles become rooted in the basal layer of the skin, near blood vessels, in order to absorb nutrients.
Hair can grow up to 90 cm long during the growth stage.

Structure of Hair Follicles

The hair follicle is the site where hair is produced.
Below the follicle is the hair bulb, a group of active cells that enable hair growth through continuous cell division.
At the base of the hair bulb is the dermal papilla, which contains capillaries and nerves that supply nutrients to the growing hair.
Once the dermal papilla degenerates or is damaged, hair growth stops and the hair gradually falls out.

Arrector Pili Muscle

The arrector pili muscle is a small muscle attached to the hair follicle. When it contracts, it causes the hair to stand upright, commonly known as “goosebumps.”

Sebaceous Glands

Sebaceous glands are responsible for secreting sebum. When sebum mixes with sweat, it forms an emulsified lipid film that moisturizes and protects the scalp and hair, inhibits the growth of microorganisms on the scalp, and neutralizes alkaline substances present on the scalp.

However, sebum secretion changes with age. Androgens, progesterone, and adrenal cortical hormones all affect sebaceous gland activity and can lead to hair loss. In addition, excessive consumption of meat, fats, and medications (such as steroids) can also influence sebum secretion.