Skin, Hair, and Nails - Hair and nails

Certainly the most noticeable of the specialized forms of skin are our hair and nails. What we see of them is really a dead tissue, called keratin , similar to the dead skin cells that are continually being shed by our bodies, but much more firmly packed together. However, hair and nails both originate in cells that are very much alive—as anyone who has plucked a group of hairs or suffered the pain of a torn-out nail knows very well. Growth occurs in this living region, with new cells pushing the dead, hard hair and nail stalks upward, then dying themselves and being replaced from below.

The bottom end or root of a hair is lodged, as noted above, in a follicle , a hollow resembling a rounded bottle with a long, narrow neck slanting toward the skin's surface. Each follicle is supported by the little hummock of a papilla, and is serviced by tiny oil glands that lubricate the shaft (or neck) through which the hair pushes toward the surface.

The follicles of the long hairs of the scalp, groin, and armpits may be found deep in the subcutaneous layers of the skin; others are no deeper than the top layers of dermis. Attached to a follicle are microscopic muscle fibers that, if stimulated by cold or emotional factors, can contract around the follicle; the result is goose-flesh or sometimes even the sensation that our hair is standing on end.

A nail's living, growing part is found beneath the whitish half moon, or lunula , at its base. The lunula is sometimes obscured because a layer of epidermis (cuticle) has grown over it. Except at its very top (the part we can trim without pain), the nail is firmly attached to the ridged upper layer of the dermis, a region richly laced with tiny blood vessels.