Guide to physical urticarias

The physical urticarias are a unique subgroup of chronic urticarias in which wheals can be reproducibly induced by a physical stimulus. Cold, heat, pressure, vibration, light, water, exercise, and increases in core body temperature have ail been demonstrated as provoking stimuli. Physical urticarias comprise up to 17% of chronic urticarias (Champion et al. 1969) and occur more frequently in young adults. The physical urti&as are distinguished by the appearance of episodic lesions often limited to the areas of inciting physical stimuli. In some patients, more than one type of physical urticaria may be present. The urticarial lesions are likely due in part to mast cell activation and mediator release. Mast cell mediators, especially histamine, have been demonstrated in draining venous blood and in tissue fluids obtained from urticated areas in patients with various forms of physical u&arias. The mechanism by which a physical stimulus to the skin releases mast cell mediators is not fully understood. It may be a direct effect by an unknown mechanism or may be immunologically mediated. In some forms of physical urticaria, a passive transfer factor (usually IgE) in the serum has been reported. The important diagnostic and therapeutic features of each of the most common physical urticarias are detailed in this article.