Skin is described as sclerotic when it has lost its suppleness and can no longer be folded. Sclerosis is usually associated with atrophy (“scleroatrophy”), as observed in scars for example. Widespread sclerosis is disabling. Depending on its location, it can lead to significant reduction in respiratory or articular amplitudes, thus causing definite functional impairment. The mouth opening can be reduced and sexual activity may be impossible. Secondary and lesional localized sclerosis, such as in certain carcinomas (e.g., morpheiform basal cell carcinoma), must be distinguished from primarily sclerosing disorders such as systemic sclerosis. One of the first signs of acrosclerosis in a patient with systemic sclerosis is the decline and subsequent disappearance of palmar creases on the dorsa of the second phalange. Cutaneous sclerosis can be the manifestation of intoxication. Hence, exposure to toxic substances must always be looked for through history taking (silica, cocaine, etc.). Neonatal scleroses are caused by rare disorders that are listed in Table 40.1.