Skin, Hair, and Nails: The Basics |
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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.
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