When Plants Attack: Diagnosing and Managing Phytodermatoses

At the 2024 Dermatology Days of Paris conference, a session focused on phytodermatoses, a group of skin conditions caused by plant exposure. These conditions can induce two types of reactions: Irritation, which may be reported to Poison Control Centers under toxicovigilance, and allergy, which falls under the purview of cosmetovigilance and may be reported to the French Agency for Food, Environmental and Occupational Health & Safety.

Irritant Phytodermatoses

Irritant phytodermatoses occur when the skin or mucosal membrane is exposed to the plant, causing irritation or skin reactions without allergic sensitization. These reactions can be classified into four types:

• These reactions may be mechanical, caused by physical contact that causes irritation, such as sting or cuts. Most lesions are nonspecific; however, distinct cases include reactions to irritating plant structures. Examples include glochids from cacti, which are fine prickles that detach at the slightest touch, and hair-like structures (trichomes) on the leaves, stems, or flowers of certain plants such as barley and borage.
• Irritative phytodermatoses can be caused by several chemical agents released by plants when damaged. For instance, ivy leaves release saponins and formic acid, which can cause reactions in sensitive individuals. Some plants such as buttercups and clematis produce characteristic linear vesicles and blisters upon contact.
• Contact urticaria can be nonimmunological, as seen with nettles, which rapidly cause painful papules due to the release of histamine, acetylcholine, and 5-hydroxytryptophan. In some cases, delayed urticaria may develop days after exposure.
• Photodermatoses occur when plants release photosensitizing substances, particularly furocoumarins, which cause skin reactions upon exposure to sunlight. Symptoms, including persistent pigmentation, often appear within 24 hours but can emerge sooner and are reactivated by exposure to the sun. Common examples include reactions to plants such as fig, rue, citrus, parsley, wild carrots, and parsnips. Diagnosis is generally simple. Patients using essential oils containing photosensitizing substances should dilute them appropriately and avoid sun exposure for at least 12 hours after application to prevent adverse reactions.

Allergic Phytodermatoses

Allergic phytodermatoses are caused by a wide variety of plants and are particularly common among professionals who frequently handle them, such as florists, cooks, horticulturists, and market gardeners). Individuals who use plant-based products, including essential oils, massage oils, or medicinal plants like balsam of Peru, are also at risk.

Symptoms can vary widely, ranging from acute or chronic eczema to erythema multiforme. The location of lesions depends on the type of contact. For example, airborne allergens primarily affect the face and must be differentiated from photoallergens.

Patch testing using standard European or specialized allergen sets can help identify the causative allergen. Direct testing with the suspected plant is also an option but requires precise botanical knowledge to minimize the risks for toxicity, irritation (leading to false positives), or severe allergic reactions.

Diagnosing Phytodermatoses

Phytodermatosis is diagnosed on the basis of the type, intensity, and distribution of lesions. Other factors, such as location of contact, weather conditions, season, and patient occupation, also provide valuable insights. Symptoms of immediate hypersensitivity typically appear within an hour of exposure, while irritant dermatitis appears within 24 hours. Delayed hypersensitivity symptoms occur after 24 hours.

Two online tools are available to assist practitioners in diagnosing plant-induced dermatoses. The Botanical Dermatology Database is a comprehensive Canadian-French resource offering detailed information on a wide range of plant-induced skin conditions, making it ideal for clinicians seeking detailed information. Another tool, Botaderma, is a free and user-friendly website created by dermatologist Jean-Claude Rzeznik and botanist Yves Sell, PhD. This tool helps to identify plants responsible for dermatitis in France by combining clinical examination and patient history to guide the diagnostic process.

This story was translated fromUnivadis France using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.