The sunburn cell, with its pyknotic nucleus and eosinophilic cytoplasm, is characteristic of mammalian epidermis after exposure to UVC and UVB radiation or UVA radiation in the presence of psoralens. The photochemical events that lead to its formation are not known, but there is good evidence that damage to DNA is an important factor. The fate of the sunburn cell, a keratinocyte which shows abnormal and premature keratinization, is not known. Desquamation and/or phagocytosis seem probable. Sunburn cells may be regarded as examples of apoptosis: controlled individual cell death.