Repetitive frictional insults over years to human skin result in lichenification, callosites, and clavi (corns). No measurements of the forces involved have been made for callosites or corns. Two reports deal with lichenification produced by repeated rubbing over weeks. By contrast, friction blisters have been seriously studied because they can be produced in minutes and because foot blisters can disable soldiers. Three devices to measure the coefficient of friction of materials on man's skin and eight machines to rub man's skin are reviewed.