They include thickening, brittleness, discolouration, and ingrown toenails. Nails, like hair, are an appendage of the skin. They are formed by layered sheets of protein with traces of other substances. Contrary to popular belief, there is very little calcium in nails. The normal toenail may be from 0.05 to 1.0 mm thick,. and grows its full length in about six to twelve months.
Nails are harder than skin, due to their high sulfur content and lack to water.
The normal nail is translucent, and one can see the underlying pink nail bed. Thickening and discolouration are often the sign of a diseased nail. With aging, the toenails thicken, grow more slowly, and become more susceptible to disease. Injury, infection, and disease may affect the toenails. The toenails and surrounding tissues are are susceptible to day to day small repetitive injuries, for example in confining shoes.