Lemons share the skin-irritating limonene oil and histamine-releasing properties of other citrus fruits, but they carry an additional unique risk: phytophotodermatitis, sometimes called 'margarita dermatitis.' Lemon juice contains chemicals called furanocoumarins that, when they contact skin and are then exposed to sunlight, cause a painful burn-like rash appearing 24–48 hours later. This commonly happens when preparing drinks with fresh lemon outdoors. The rash can leave dark marks lasting weeks or months.

For people with eczema, this UV-activated chemical reaction on already-compromised skin can be particularly severe. The risk is highest with fresh-squeezed juice and zest, as commercially processed lemon products have lower furanocoumarin levels.