Hair is a filamentous structure made of keratin, a protein, that grows from follicles located in the skin. Each strand of hair consists of a shaft (the visible part above the skin) and a root (embedded within the follicle).

Hair structure consists of three main parts: the medulla, which is the innermost layer; the cortex, which provides strength, color, and texture; and the cuticle, the outermost protective layer that shields the hair from damage.

Hair has two parts, the hair follicle and the hair shaft. Other than this hair is composed of a structural protein keratin. It also contains carbon, oxygen, hydrogen, nitrogen, and sulfur. The living and generative part of the hair is known as a hair follicle. Whereas the non-living part of the hair is seen above the skin is the hair shaft.

The word "hair" usually refers to two distinct structures: the part beneath the skin, called the hair follicle, or, when pulled from the skin, the bulb or root. This organ is located in the dermis and maintains stem cells, which not only re-grow the hair after it falls out, but also are recruited to regrow skin after a wound.