Normal skin can resist mechanical insults to a certain degree. If not counteracted by protective measures, excessive friction or superficial skin injuries may develop into cutaneous disease. Posttraumatic eczema can persist or recur for long periods of time, while preexisting dermatoses can be aggravated by mechanical trauma. If a dynamic relationship between trauma and development of eczema is made probable, it has important medical implications when job related. Only a minor fraction of individuals exposed to repetitive mechanical stimuli such as friction develop physical irritant contact dermatitis, indicating a probable role of genetic predisposition in addition to environmental factors such as temperature and sweat production. Hyperkeratoses, calluses, and lichenification are common clinical manifestations of a frictional eczema which most often involves the hands. Frictional hand dermatitis can be caused by working in various occupations, from office workers to craftsmen such as carpet installers and shoe makers. Time from onset of exposure to development of frictional dermatitis can vary from weeks to years. Posttraumatic eczema following mechanical injury usually occurs within weeks. It may occur in association with an underlying endogenous dermatosis (isomorphic reaction of Koebner’s phenomenon) or occur as an isolated idiopathic reaction. The clinical features of posttraumatic eczema are indistinguishable from other types of hand eczema. Core Messages