The skin is constantly subjected to both internal and external mechanical forces, so that for experimental purposes it may be impossible to determine what constitutes the normal resting state. These forces are likely to be as important in the maintenance of the structural integrity of the connective tissues of the skin [1,2] as they are with bone, which becomes demineralized during the protracted absence of normal gravitational force during space travel [3]. In contrast to events in the whole organism, isolated human dermal fibroblasts in culture make more collagen when subjected to reduced gravity [4]. Many normal biochemical functions of the skin are dependent on appropri-ate mechanical forces, and when these become excessive, as in lymphoedema, protease inhibitors are released with many deleterious consequences [5].Healthy skin is well adapted to resist the adverse effects of a wide range of mechanical injuries [6]. These include friction, pressure, contusion, laceration, suction and vibration. The clinical consequence of injury will depend on characteristics of the noxious stimulus, such as its intensity and duration. Factors related to the skin also influence the response; thus, the same degree of friction may produce a blister in one person but no visible change in another. Time is required for adaptive responses, such as callus formation and lichenification, to occur.