I have hard white bumps, like warts, spreading on my legs, arms, hands, and ankles. They started with two on my hand about five years ago.

Hi When you say bumps, are these elevated or raised? Or are these more like spots which are actually flat? Are these bumps scaly or shiny? A differential will be lichen planus. "Lichen planus appears as shiny, flat-topped bumps that often have an angular shape. These bumps have a reddish-purplish color with a shiny cast due to a very fine scale. The disease can occur anywhere on the skin, but often favors the inside of the wrists and ankles, the lower legs, back, and neck." Source:http://www.aocd.org/skin/dermatologic_diseases/lichen_planus.html Other differentials for whitish bumps may be milia, warts, molluscum and keratosis pilaris. Milia may be likely here. This commonly affects the face and the hands and it manifests as a firm bump which may be filled with a whitish material almost like molluscum. You may need to have this assessed by a doctor. Warts and molluscum are characteristic and both conditions are contagious. They may also be chronic with molluscum resolving spontaneously in some cases.