What is it about hogweed — and lemons and limes — that can cause burns?

When exposed to sunlight, chemicals in the juice and sap damage DNA

giant hogweed plant

SAP + RAYS = BURN The giant hogweed contains chemical compounds that, when activated by sunlight, can burn exposed skin. The plant is in the Umbelliferae family, which also counts celery, carrots, parsnip, dill and fennel as members.

Salicyna/Wikimedia Commons (CC BY-SA 4.0)

Another warning to add to the summertime list: check for ticks, go inside during lightning … and hands off the giant hogweed. Getting the plant’s sap on the skin, along with exposure to sun, can lead to severe burns.

All good advice, but the invasive plant, which looks like Queen Anne’s lace on steroids, and was recently spotted in Virginia, isn’t the only vegetation that contains the burn-causing chemical compounds. Furocoumarins can be found in the fruit and vegetable bins of most refrigerators. Limes, lemons, parsnip, fennel, dill and members of the mulberry family are some of the plants that have furocoumarins.

The chemicals make the skin more prone to sunburn. It takes from 30 to 120 minutes for the skin to absorb furocoumarins from the plant’s juice or sap. With sun exposure, ultraviolet A radiation activates the chemical compounds, which then bind to and damage DNA. Those cells with the damaged DNA die, leaving behind a burn. The condition is called phytophotodermatitis. (The popular summertime combo of Mexican beers with lime has led to another moniker: Mexican beer dermatitis).

burns from lemon juice and sun exposure
THE PRINT MATCHES The thigh of a 13-year-old girl who had been squeezing lemons into her family’s drinks at the beach reveals burns corresponding to the shape of her hand. J.F. Moreau, J.C. English III and R.P. Gehris/Journal of Pediatric and Adolescent Gynecology 2014

Pediatric dermatologist Robin Gehris  of the Children’s Hospital of Pittsburgh sees phytophotodermatitis “at least once a week” in her practice during the summer, most commonly from limes and lemons, she says. The reaction only happens where juice or sap touches the skin; a dribble of juice will leave a streaky mark. A hand covered in lime juice could leave its likeness on a leg. “Often, the pattern is one of the things that keys us in,” Gehris says. How bad the burn is depends on how much juice or sap and how much sun; a lot could lead to blistering. The best prevention? Rinse off juice-covered hands and plant-touching explorers.

Aimee Cunningham is the biomedical writer. She has a master’s degree in science journalism from New York University.

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