ON AN URTICARIAL RESPONSE TO LIGHT AND ITS PHOTOPHYSIOLOGY 1

Abstract

A white man aged 20 yrs. develops a marked urticarial reaction in areas of skin exposed to sunlight for as short a period as 3 min. Light in the blue and violet portion of the visible spectrum, i.e., between 3900 and 5300 A, is responsible and the patient reacts with normal delayed erythema and pigmentation to ultraviolet. The reaction strongly resembles the "triple response" described by Lewis. It may be due to the production of a histamine-like substance following the photoactivation of a particular kind of light absorbing molecule. This reaction as well as other types of photosensitivity as represented in hydroa aestivale, eczema solare, lupus erythematosus, etc. requires further study, particularly with reference to the wave lengths of light responsible, since one etiologic factor in any photosensitization must be a photoactive compound capable of absorbing the offending light rays.