Experimental investigations on the trigger mechanism of the generalized type of heat and cold urticaria by means of a climatic chamber.

The physical conditions of challenge were investigated in a climatic chamber on 8 patients with cholinergic urticaria and 10 patients with generalized cold urticaria. The cholinergic urticaria was induced by passive or active (physical exercise) heating and psychological stimulation; the generalized cold urticaria was induced by general cooling at rest and during physical effort. The ambient temperature was varied, and the mean body temperature was recorded continuously at different measuring points. The experiments revealed that in both types of urticaria the physical trigger mechanism seems to be strictly related to thermoregulatory processes; the crucial point is neither the actual temperature of the skin surface, the average skin temperature, nor even the "core" temperature, but a rise or fall in the weighted average body temperature. In cholinergic urticaria it was not relevant whether skin lesions were provoked by passive heating of the body at rest (sauna-like conditions) or by active heating at low ambient temperature. A basically different challenge mechanism must be assumed therefore in the generalized type of heat and cold urticaria, in contrast to their localized contact types.