Pathomechanisms in physical urticaria

Various exogenous stimuli, e.g., rubbing, pressure, cold, heat, or electromagnetic waves, have been described to elicit whealing reactions, the so-called physical urticarias. They may occur as isolated diseases or in association with other types of urticaria. In many cases, the respective physical factors can be defined exactly, e.g., the degree of temperature changes or the range of eliciting ultraviolet wavelengths. In contrast, the underlying pathomechanisms are mostly still obscure. In the past, often contradictory results have been reported regarding the role of IgE, complement factors, histamine, or even mast cells. Recently, many investigations have been performed on solar urticaria where subgroups of patients with different clinical and pathophysiologic features could be defined and mechanisms of tolerance induction have been studied that also offered an efficient treatment modality. Therefore this review will mainly focus on this type of disease as a paradigm of the pathomechanisms of physical urticaria.