Adverse Skin Reactions to Plants and Plant Products

Abstract

Plants are a significant cause of skin reactions worldwide. Because most affected individuals do not present to a dermatologist, it is likely that skin reactions to plants are under-reported. Plants may induce mechanical irritant reactions, e.g., due to spines or hairs. Trauma to the plant may release chemical irritants such as calcium oxalate crystals or phorbol esters. Skin contact with furocoumarins in some plants, notably members of the Apiaceae, followed by exposure to ultraviolet A, induces a characteristic streaky rash leading to hyperpigmentation (phototoxicity). A few plant species including nettles (Urtica spp.) inject toxins into unsuspecting predators, a form of chemical warfare. These toxins include histamine, inducing nettle rash (urticaria). Other nonprotein plant constituents such as cinnamic acid derivatives may induce urticaria by a pharmacological mechanism. However, some individuals may develop immunologically mediated urticaria and even anaphylaxis caused by immediate hypersensitivity to plants or plant products, including fruit, vegetables, and nuts. Finally, a few plant families have the potential to induce allergic contact dermatitis; these include the daisy family (Asteraceae/Compositae) and poison ivy family (Anacardiaceae)