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Author: Vanessa Ngan, Staff Writer, 2006.
Drug-induced photosensitivity occurs when certain photosensitising medications cause unexpected sunburn or dermatitis (a dry, bumpy or blistering rash) on sun-exposed skin (face, neck, arms, backs of hands and often lower legs and feet). The rash may or may not be itchy.
Medications can also cause onycholysis (the nail plate lifting off the nailbed). This is known as photo-onycholysis.
Drug- and chemical-induced photosensitivity occurs when a drug or chemical agent combines with UV radiation to cause a phototoxic or photoallergic reaction. These agents are called photosensitisers and can be topical agents or medications that are taken orally. The following table lists the most common medications and topical agents causing photosensitivity.
The clinical features of drug-induced photosensitivity vary according to the photosensitising agent involved and the type of reaction it causes in the skin. The reaction can be phototoxic and/or photoallergic.
Phototoxic reactions result from direct damage to tissue caused by light activation of the photosensitising agent, whilst photoallergic reactions are a cell-mediated immune response in which the antigen is the light-activated photosensitising agent.
Photoallergic reactions occur less commonly than phototoxic reactions and are mostly caused by photosensitising topical agents. Although some oral photosensitising medications can cause photoallergic reactions, most cause phototoxic reactions. A handful of medications can cause both phototoxic and photoallergic reactions.
The clinical features differ between phototoxic and photoallergic reactions.
The main goal of treatment is to identify the photosensitising agent and if possible to avoid it. In cases where medication is being taken to treat an existing condition and cannot be discontinued, patients should be advised to follow strict sun protection strategies, including wearing sun protective clothing and using high protection-factor, broad-spectrum sunscreen.
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