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Author: Dr Ian Coulson, Consultant Dermatologist, East Lancashire NHS Trust, UK. Copy edited by Gus Mitchell. November 2021.
Phytophotodermatitis, a form of plant dermatitis, is a skin reaction that occurs after natural photosensitising chemicals (furanocoumarins) present within plant sap and fruits, become smeared onto the skin, and there is subsequent exposure to sunlight.
The areas affected become acutely red, and often blister. Skin lesions may be linear or streaked in morphology. After the acute inflammatory reaction subsides, there is typically postinflammatory hyperpigmentation which may last for years.
Phytophotodermatitis can develop in anyone. It is not an allergy, and accidental contamination of the skin with the juice or sap from a causative plant, followed by sun exposure, may induce the reaction.
Individuals at greater risk include:
Many plants contain furanocoumarins, which are responsible for the acute phototoxic reactions. Ultraviolet A radiation (UVA) interacts with the furanocoumarin, producing cell membrane damage and inflammation.
Local accidental smearing of plant sap onto the skin followed by light exposure is the most common type of reaction; ingestion of plants rich in furanocoumarins cause a more generalised photosensitivity. The reaction is a direct toxic effect and does not involve the immune system.
|Botanical name||Common names|
|Umbelliferae||Ammi majus||Queen Anne's Lace|
|Heracleum spondylium||Cow parsnip|
|Heracleum mantegazzianum||Giant hogweed|
Gas plant, burning bush of Moses
|Moracea||Ficus carica||Fig (from sap, not fruit)|
Approximately 24-48 hours, after exposure to ultraviolet radiation from sunlight, the area of skin contaminated by the photosensitising sap/juice becomes red, inflamed, and often blisters. Ulceration may occur, the area will scale, and then heal after several weeks to leave postinflammatory pigmentation, which may last for several years.
There are several possible patterns of reactions:
Postinflammatory hyperpigmentation may be more intense in skin of colour.
The history of accidental exposure to causative plants combined with the clinical appearance is diagnostic.
The use of a sunscreen with high UVA protection in addition to covering the skin to prevent further light exposure may diminish the severity of the reaction if it is commenced as soon as the accidental exposure is recognised.
Provided offending plants can be recognised and avoided, it should not recur. Occupational phytophotodermatitis in vegetable pickers can be avoided by wearing appropriate gloves. Those using “strimmers” should protect themselves using a visor and protective clothing.
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