Phototoxicity and photoallergy – A brief review on pathogenesis, recent advances, and approach to a patient with photosensitivity

Abstract

Photosensitivity can result in phototoxic or photoallergic reactions. Phototoxicity is the more frequent of the two and could be acute or chronic. Clinically, erythema and edema are the hallmarks of acute phototoxic reactions. There are two mechanisms by which phototoxic reactions can happen; photodynamic (which is oxygen dependent) and non-photodynamic (which is oxygen independent). Ultraviolet B (UVB) and less effectively UVA can cause phototoxic reactions. The main action spectrum for chronic phototoxicity falls in the UVB range, as compared to the UVA rays. Other phototoxic reactions include lichenoid or lichen planus such as reaction and photo-onycholysis. Photoallergic reactions usually are due to delayed hypersensitivity reaction that manifests with papular or eczematous eruptions. Topical medications are typically the most frequent provoking cause of photoallergic skin lesions. A thorough history with detailed clinical examination is necessary for the management of photosensitivity. Availability of newer diagnostic techniques and treatment modalities gives a promising approach to the management of photo-aggravated dermatoses.