a cutaneous neoplasm caused by ionizing radiation, certain genetic defects, or chemical carcinogens, including arsenics, petroleum, tar products, and fumes from some molten metals, or by overexposure to the sun or other sources of ultraviolet light. Skin cancers, the most common and most curable malignancies, are also the most frequent secondary lesions in patients with cancer in other sites. Risk factors are a fair complexion, xeroderma pigmentosa, vitiligo, senile and seborrheic keratitis, Bowen's disease, radiation dermatitis, and hereditary basal cell nevus syndrome. The most common skin cancers are basal cell carcinomas and squamous cell carcinomas. Tumors of the sebaceous glands or sweat glands occur infrequently and are adenocarcinomas. Basal cell carcinomas, typically raised, hard, reddish lesions with a pearly surface, do not metastasize, in contrast to scaly, slightly elevated squamous cell tumors that may become exophytic, friable growths with extensive ulceration and a nonhealing scab. A definitive diagnosis may be established by incisional biopsy or by excisional biopsy, which may be the only treatment required for small lesions. Surgery is usually indicated if the lesion is large, if bone or cartilage is invaded, or if lymph nodes are involved. Radiotherapy may be preferable for some smaller facial lesions and is commonly recommended for the treatment of skin tumors without distinct margins. Because of the possibility of recurrence of cancer, surgery is favored for the treatment of younger patients. Topical zinc chloride may be used in treating fairly common recurrent skin cancers; topical 5-fluorouracil is recommended for refractory premalignant actinic keratosis and for superficial basal cell carcinomas. An immunotherapeutic method is based on the induction of delayed hypersensitivity and consists of painting the lesions with a cream containing dinitrochlorobenzene (DNCB) and triethylene-immuno-benzoquinone (TEIB). Despite the curability of skin cancer, it causes many deaths because people fail to obtain treatment. Lesions caused by actinic rays may be prevented by applying a sunscreen containing paraaminobenzoic acid (PABA).