In the West, there is a general acknowledgment that the appearance of one's nails can reflect the state of one's health, but in many Eastern medical traditions the nails are used quite directly in the diagnosis. Despite their role as protective shields for the fingertips, nails are actually more sensitive to internal and external conditions than one might imagine.

If you have thought of them primarily as canvases for the display of interesting colors of nail varnish, the following may surprise you -- and perhaps lead you to keep them unpainted from time to time, so you can read them for clues.

First, some basic facts: Nails, like hair, are made of the protein keratin. The visible part of the nail is called a nail plate. The skin underneath the nail plate, which contains elastic fibers that hold the nail firmly in place, is called the nail bed; in the lower part of the nail bed is the matrix from which the nail cells divide, causing the nail plate to grow.