Exposure to sunlight, particularly ultraviolet light (UV), can produce changes in the status of the immune system. Photoimmunology is the study of the distortions in "normal" immune responses that may be produced by UV and/or visible light exposure. Photoallergy, on the other hand, is an acquired im-munologically mediated reactivity to a chemical or drug precipitated by the formation of photoproducts. This article reviews the key principles with supporting evidence from both photoimmunology and photoallergy. Reviews of the fundamental concepts of cutaneous structure and function, inflammation, immunology, and allergic contact dermatitis are presented as introduction. Subsequent sections discuss the capacity of UV to alter allergic contact dermatitis. The second part of the article presents an overview of past clinical observations and important laboratory animal studies relevant to photoallergy, including new techniques for predictive testing for photoallergic contact dermatitis in animals and helpful suggestions for handling problems when assessing consumer products for photoallergenicity. The article concludes by presenting approaches to diagnosing patients with suspected photoallergic contact dermatitis and photosensitivity to chemicals and drugs.
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