Photodermatoses are caused by an abnormal reaction mainly to the ultraviolet component of sunlight. Photodermatoses can be broadly classified into four groups: immunologically mediated photodermatoses, chemical- and drug-induced photosensitivity, photoaggravated dermatoses, and DNA repair-deficiency photodermatoses. In this review, we focus mainly on chemical- and drug-induced photosensitivity, namely, phototoxicity and photoallergy.
Photosensitivity can be caused by many different topical or systemic exogenous agents. These agents are usually compounds with unsaturated double bonds, which absorb ultraviolet A wavelength energy. Drugs and chemicals that are most frequently responsible for phototoxic and photoallergic reactions will be discussed briefly. Pathophysiology, clinical manifestations, and histopathologic investigations of both phototoxicity and photoallergy are summarized separately. The main differences between these two entities, including clinical appearance, pathophysiologic mechanisms, and time of onset, will be emphasized.
Photosensitivity is a challenging area of dermatology, with a wide range of morbidities, both for the physician and the patient. For the exact diagnosis and precise control of photosensitivity, a systematic approach is vital. Avoidance of direct sunlight and sun-tanning facilities, as well as photosensitizing agents, usage of clothing with ultraviolet filters, and appropriate sunscreen can all minimize the risk for photosensitivity effects. A combination of measures, including phototherapy in different modalities and topical and systemic drugs, can be beneficial in the management of photodermatoses.