Detailed information about anatomy of human hair

Hair Anatomy

Apart from enhancing looks and appearance, hairs are also responsible for sensory transmission in the human body. Human skin contains approximately 2 million hair follicles. Hairs grow from pockets in the skin called hair follicles.

Though there are several parts making up the anatomy of human hair, it has predominantly two separate structures - the follicle in the skin that makes the hair and the shaft of the hair itself.

Hair follicles

Hairs take birth in a sac-like structure called a hair follicle that surrounds the hair root and is found below the skin. The average human head has about 100,000 hair follicles. Sebaceous glands surrounding the hair follicle secrete sebum and oils into the hair follicle canal.

The sebaceous gland is extremely important as it produces sebum which protects the hair and is a natural conditioner. Too much or two little production of oil from this gland causes oiliness or dryness in the hair and scalp.

At the base of a hair follicle is the hair root. During the growing phase, the follicle has a bulb-shaped bottom, in the center of which is called the dermal papilla. The papilla contains small blood vessels, which bring it food and oxygen and takes away waste. Pigmented cells growing on top of the dermal papilla determine the color of hair.

Separate structures in the skin called sweat glands secret salt-water. We have about 3 million sweat-glands in our skin. When it becomes too hot, the sweat glands regulate the temperature of hair and body by secreting sweat. The sweat glands are completely separate from the hair follicle structures that make hair fiber.

Hair shaft

Anatomy of human hair shaft consists of 3 layers:

  • The innermost layer is called the medulla. It is present only in large thick hairs like the ones on our scalps. It helps giving hair its elasticity.
  • The middle layer is called cortex. It constitutes the bulk of the hair. It’s the cortex which is responsible for providing hair its structure, strength, color and texture to the hair.
  • The outermost layer is known as cuticle. It’s thin and transparent. It protects the inner structure of the hair.

Hair follicles consist of the following key components:

Inner root sheath

The inner root sheath (IRS) does not contain any pigment. It is comprised of three parts; the henley layer, huxley layer, and cuticle layer. The cuticle is the innermost portion that touches the hair shaft. The inner sheath follows the hair shaft and ends below the opening of a sebaceous gland and sometimes an apocrine gland.

Outer root sheath

The outer root sheath (ORS) is coated over the IRS from the lower end of the hair bulb to the entrance of the sebaceous gland duct. It connects the hair follicle seamlessly to the skin epithelium.

Fibrous root sheath

It is the outermost layer of the hair follicle surrounding the vitreous layer. It is comprised of thickened collagen bundles that coat the entire hair follicle.

Suprabulb region

Consisting of components of hair shaft, vitreous layer, ORS, IRS, and the fibrous root sheath; suprabulb region starts from hair bulb and ends at the isthmus of the hair follicle.

Isthmus

Isthmus begins from the attachment of the erector pili muscle and goes into the entrance of the sebaceous gland duct. At this level, the IRS gets fragmented and exfoliated whereas ORS is fully keratinized.

Infundibulum

Infundibulum constitutes the upper portion of the hair follicle and it is surrounded by the surface epidermis.