Diseases of the skin caused by or made worse by exposure to sunlight. In sufficient dosage, shortwave ultraviolet light (UVB always causes erythema. Higher doses progressively cause oedema and blistering; this is acute sunburn. Graduated exposure to UVB causes pigmentation (tanning). Prolonged chronic exposure to sunlight eventually accelerates ageing of the exposed skin with lentigo formation and loss of collagen and elastic tissue. After decades of such exposure, epidermal dysplasia and cancer may supervene.