Description, Causes and Risk Factors:

Alternative Name: Strimmer's rash, margarita dermatitis.

Abbreviation: PPD.

Phytophotodermatitis is a common cutaneous phototoxic reaction. Contact with plant-derived phototoxic substances (furocoumarins or psoralens) followed by sunlight exposure produces the clinical lesions. These phototoxic substances are found in various vegetable families.

Phytophotodermatitis is more common is people who handle fruits and vegetables for a living such as bartenders, grocers or agricultural farm workers. Children can develop this rash if they play in certain grasses belonging to the same family as Queen Anne's lace.

When the skin is exposed to sunlight, UVA (between 320-380nm) strikes the psoralen and energy is absorbed. This raises the psoralen from the ground state to an excited state. As it returns to the ground state the energy is released as heat, fluorescence and/or phosphorescence. Two separate toxic reactions lead to cell death. Firstly, an anaerobic reaction in which the excited psoralens bind to RNA and DNA, and secondly, an aerobic reaction in which the excited psoralens cause cell membrane damage and edema.

The common culprit plant families are the Apiaceae (Umbelliferae), Rutaceae, and Moraceae. Some of the common names of the plants involved for the Apiaceae family are Queen Anne's lace, cow parsnip, celery, spring parsley, parsnip, and giant Russian hogweed. For Rutaceae, these are the bergamot lime, burning bush, and gas plant. Figs are the culprit in the family Moraceae. St. John's Wort (family Hypericaceae) has also been implicated. The most common phototoxic compounds are the furocoumarins (e.g., psoralen, 8-methoxypsoralen, and 5-methoxypsoralen).

Sometimes, the use of certain drugs (sulphonamides, antidiabetics, thiazides, non-steroid anti inflammatory drugs, phenotiazines) or contact with oils, tars can also induce sensitization to solar UV20. Phototoxic and photoallergic dermatitis can also be induced by airborne allergens and irritant substances in the form of solid particles, gases or droplets.


The rash typically appears between 24-72 hours afterexposure. The affected area can have a very clear line ofdemarcation where unaffected skin has been protected byclothing; such as an `inverse' stocking distribution if the patientwas barelegged but wearing socks at the time of exposure to thepsoralen.


The diagnosis of phytophotodermatitis is not always easily established. It is important to differentiate phytophotodermatitisfrom impetigo, allergic dermatitis, and frompseudo-phytophotodermatitis caused by contact with plantinsecticides and herbicides.

Your dermatologist may be able to organize allergy testing (patch tests).Do not test for reactions to the most strongly allergenic plants because the tests could themselves create a new allergy.


Treatment is symptomatic with vigilance for secondary infection as the blisters burst. As the rash subsides it usually leaves areas of localized hyperpigmentation; this may take some weeks to fade. Wear sunscreen to reduce the amount of UV light exposure you get from the sun.

Topical steroids, and sometimes by oral steroids may be necessary to treat the rash. If there are blisters, compress the areas for 15 minutes twice daily with a mixture of a tablespoon of white vinegar in a litre of water. Ice packs or cold showers will temporarily relieve itching. Steroids are less effective when the skin is blistered. Avoid soap as it irritates.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

Reference and Source are from:

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.


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