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 structure refers to the thickness of the strands of hair. A person’s hair can be: fine medium coarse According to the World Trichology Society (WTS), hair thickness varies depending on the person. Some people have finer hairs than others. The WTS also notes that the hair fibers become shorter and finer as a person ages.

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).

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.