Careful with that lime

By Dr. Joel DeKoven

Photosensitizing compounds in citrus juice, fruits and plants can result in temporary hyperpigmentation and painful blisters

You’re on holiday, relaxing in the sun. You pick up a bottle of Mexican beer, put a lime wedge into it and shake the bottle – accidentally spraying lime juice and beer on yourself in the process. After continuing to spend the rest of the afternoon in the sun, you notice bizarre brown blotches and markings on your chest and abdomen.

What you’re experiencing is phytophotodermatitis, a reaction between the chemicals in the lime juice and sunlight that can result in temporary red, blistered or hyperpigmented skin.

Just what is phytophotodermatitis?

Phytophotodermatitis – also called Mexican beer (or margarita) dermatitis – happens when certain plant chemicals called furocoumarins or psoralens come in contact with the skin, making that area light sensitive. A skin reaction occurs when the area is then exposed to ultraviolet light from the sun.

The juice of lime and other citrus fruit is a common cause of this condition. But skin contact with certain weeds and edible plants – such as giant hogweed, meadow grass, figs, carrots, parsnips, fennel, dill, anise and celery – can also trigger a reaction.

People may have unusual patterns on their skin where they’ve come into contact with lime juice or other sources of the culprit chemicals. This can be a real puzzle and cause for concern when, seemingly out of the blue, odd shapes appear on the skin. These shapes sometimes include outlines of a handprint or fingerprints on the exposed area. The reaction doesn’t always happen the same day, which can make the symptoms even more puzzling; some people may only notice them for the first time on the plane ride home from a vacation in the sun.

In severe cases, there is a burning redness, and blisters can form within hours of contact with the chemicals and sunlight. The marks can be mistaken for an allergic reaction, child abuse or even jellyfish stings. After the inflammation subsides, there may still be brown marks or patches that last for weeks or months.

The sun’s UVA light is responsible for the vast majority of photoreactions that result in phytophotodermatitis. This phototoxic skin reaction is entirely independent of the immune system, so it can occur in any individual, and without prior sensitization.

Dr. Joel DeKoven is a consultant dermatologist and associate professor in the department of medicine at the University of Toronto. His clinical subspecialty interest focuses on the diagnosis and management of allergic contact dermatitis and the evaluation of complex allergic and work-related skin disease.

How can you prevent this condition?

Don’t mix drinks while in the sun. And be careful when handling citrus fruit juice.
If you come into contact with the plant chemicals, wash your skin immediately so that no traces of the chemicals remain.
If you can’t wash up, stay indoors after exposure.
Field workers and gardeners who work outdoors and handle plants that cause the skin condition should wear gloves, long sleeves and long pants.