Ear hair canal is sometimes trimmed for cosmetic reasons. Excessive hair growth within or on the ear is known medically as "auricular hypertrichosis". Some men, particularly in the male population of India, have coarse hair growth along the lower portion of the helix, a condition referred to as "having "hairy pinnae"" ("hypertrichosis lanuginosa acquisita"). Hair is a protein filament that grows from follicles in the dermis, or skin. With the exception of areas of glabrous skin, the human body is covered in follicles which produce thick terminal and fine vellus hair. It is an important biomaterial primarily composed of protein, notably keratin.
Hair cell fish have been found to regenerate, their ability has been studied at length. In addition, lateral line hair cells, which have a mechanotransduction function, have been shown to regrow in organisms, such as the zebrafish. Researchers have identified a mammalian gene that normally acts as a molecular switch to block the regrowth of cochlear hair cells in adults. The Rb1 gene encodes the retinoblastoma protein, which is a tumor suppressor. Rb stops cells from dividing by encouraging their exit from the cell cycle. Not only do hair cells in a culture dish regenerate when the Rb1 gene is deleted, but