Fototoxic

Fototoxic, also known as photosensitivity or phototoxicity, refers to an adverse skin reaction triggered by exposure to sunlight or other sources of ultraviolet (UV) radiation, particularly when certain substances are present on or in the body. This reaction is not an allergic response but rather a chemically induced irritation. The specific substance, which can be a medication, a chemical in a cosmetic product, or a plant-derived compound, absorbs UV light and converts it into a form of energy that damages skin cells.

There are two main types of fototoxic reactions: phototoxic and photoallergic. Phototoxic reactions are more common and can occur in anyone exposed to a sufficient amount of the offending substance and UV light. The reaction typically appears as exaggerated sunburn, with redness, swelling, and sometimes blistering, within hours of sun exposure. The severity is usually dose-dependent.

Photoallergic reactions are less common and are true allergic responses. They occur when UV light alters a substance, making it recognizable as foreign by the immune system. This leads to a delayed hypersensitivity reaction, often manifesting as eczema-like rashes, itching, and sometimes hives, typically 24 to 72 hours after sun exposure.

Common culprits for fototoxic reactions include certain antibiotics (like tetracyclines), diuretics, non-steroidal anti-inflammatory drugs (NSAIDs), retinoids, and some artificial sweeteners. Certain plants, such as those in the citrus family (like limes) or wild parsnip, can also cause phytophotodermatitis, a specific type of fototoxic reaction. Prevention involves avoiding sun exposure while using photosensitizing agents or using broad-spectrum sunscreens with a high SPF and protective clothing.