Demonstration of sweat allergy in cholinergic urticaria.

Twenty patients with cholinergic urticaria, 11 sex- and age-unmatched patients with acute or chronic urticaria and 20 sex- and age-matched non-atopic control subjects were skin tested with autologous sweat. All cholinergic urticaria patients showed positive immediate-type skin reactions at 2(0)-2(9) dilutions of sweat (geometric mean of maximal positive dilutions +/- S.D. was 2(4.6 +/- 2.6), while in acute and chronic urticaria only three patients showed positive reactions at low dilutions (two 2(0) and one 2(1)) and none of 20 controls showed positive reactions. Prausnitz-Küstner (P-K) tests performed with the serum and sweat from six patients were all positive at 2(3)-2(8) dilutions. Percent histamine release from peripheral leukocytes of five patients challenged with the standard sweat samples was significantly higher than in five control subjects. Histamine release from leukocytes of the patient on sweat challenging was abandoned by acid treatment of leukocytes. Leukocytes, from a healthy subject sensitized with the patient's serum, released histamine on sweat challenging. These results seem to indicate that cholinergic urticaria patients have a type I allergy to their own sweat.