Skin, Hair and Nails: The Basics

Hair

Though the hair follicles are located in the dermis (the second layer of skin), the composition and function of hair is similar to that of the top layer -- the epidermis. Hair is made of keratin, the same substance that forms nails and the barrier at the top of the skin. Cells that make keratin and melanin live at the root of the hair, where they die -- leaving their keratin and melanin to give substance and color to the hair.

Like other parts of the skin, hair helps protect the body. Eyelashes and eyebrows shield the eyes from sun, dust, and perspiration. Nasal hair helps reduce your intake of dust and other
foreign bodies. Hair on the scalp provides some insulation. However, as the human species has evolved and become more sophisticated in protecting itself from extremes of temperature, it has less need for body hair. When we get goose bumps, we are seeing an evolutionary remnant of a once-critical ability to thicken our "fur" in response to cold.

Nails

Nails are thickened and hardened forms of epidermis. Nail cells are created in the base of the nail bed and then die. Nails are composed of dead cells that are, in turn, composed of a strong form of keratin. The nail bed is alive and continuously produces new nail. Thus, a nail is simply a much harder and thicker mat of keratin than the topmost layer of skin.

Cross Section of Nail

Nails are thickened, hardened plates made up of dead cells from the epidermis, the outer layer of skin. The nail bed is alive and continuously produces new cells, which die, stick together into a hard substance, and form the nail. The cuticle protects the base of the nail from infection-causing bacteria and fungi.

Copyright 1999 © by President and Fellows of Harvard College
Reprinted with permission from the Harvard Medical School Family Health Guide, Simon & Schuster 1999. Art copyright © Harriet R. Greenfield, Newton, Mass.