Hair tourniquet

Hair root is the part of the hair that is enclosed within the hair follicle, under the skin. The hair root ends in an enlargement, the hair bulb, which is whiter in color as it lacks the pigment that gives the hair shaft its color. The hair bulb encloses the dermal papilla, which supplies nutrients to the hair and contains the germinal matrix, where new cells are produced for hair growth.

Structure[edit | edit source]

The hair root is made up of several layers, each with a specific function. The innermost layer is the medulla, followed by the cortex, which makes up the majority of the hair root, and the outermost layer is the cuticle. The cuticle is a hard, shingle-like layer of overlapping cells. Some hair, like that of many mammals, has a layer of air-filled cells within the medulla, which aids in heat retention.

Function[edit | edit source]

The primary function of the hair root is to anchor the hair into the skin. The hair root is connected to the arrector pili muscle, which can cause the hair to stand up when it contracts. This is most noticeable in animals, where it can create an "end on end" effect that helps to trap a layer of air to keep the animal warm.

The hair root also plays a role in hair growth. The cells in the germinal matrix divide and push upwards, hardening and taking on pigment as they go. This process is influenced by hormones, particularly androgens, which can cause the hair root to shrink and the hair to thin in those genetically predisposed to androgenetic alopecia.