Patients with cholinergic urticaria (CU) show a number of small, short-lasting hives when their body core temperature increases, usually during sweating following exercise or bathing. The precise mechanism(s) of hive formation in CU has been unclear except for the involvement of acetylcholine. We recently reported that most CU patients show immediate-type skin responses to their own sweat, whereas the rest of CU patients have positive autologous serum skin tests (ASSTs). The former group produced satellite wheals following acetylcholine injection, whereas the latter group produced hives in conjunction with hair follicles. We propose two subtypes of CU: 1) a sweat-hypersensitivity type with strong hypersensitivity to autologous sweat, nonfollicular hives, development of satellite wheals, and lack of positive ASST; and 2) a follicular type with follicular hives and positive ASST, but no hypersensitivity to autologous sweat or satellite wheals. We discuss the mechanisms of hive formation in these subtypes.