The major risk for outdoor workers is exposure to ultraviolet light. Other agents carcinogenic to the skin include: PAHs (coal tar, shale oil, or mineral oils); arsenic (pesticide manufacturing; sheep dip; copper, lead or zinc smelting); and ionizing radiation (radiologists); [LaDou, p. 299-302] Arsenic exposure is associated with an increased risk of basal cell cancer after a long latency. Sun exposure increases risk for basal cell cancer, squamous cell cancer, and melanoma. [Adami, p. 290-1] Chronic arsenic poisoning causes keratoses of palms and soles, patchy hyperpigmentation, and skin cancer (squamous and basal cell). [LaDou, p. 300-1; 338; 809] The evidence is strong for associations between the following agents or processes and occupational skin cancer: arsenic and compounds; coal tars and pitches; coal gasification; coke production; dibenz[a,h]anthracene; mineral oils, untreated and mildly treated; shale oils or shale-derived lubricants; solar radiation; and soots. [Siemiatycki, p. 334] Studies of ionizing radiation and skin cancer have found "meaningful associations" for Japanese A-bomb survivors, tinea capitis patients treated with radiation, and radiologists working in earlier decades. [Boice, p. 260] Scrotal cancer is a special type of squamous cell skin cancer that was first described in 1775 (chimney sweeps exposed to soot) and in 1822 (copper smelter workers exposed to arsenic). Scrotal cancer has also been reported in other workers exposed to PAHs (coke oven workers, metal lathe operators, cotton spinners, and tar distillers). [Rosenstock, p. 817-8; Mullan, p. 780-1] See "Melanoma."