莱姆病:怎么喝杯果汁就长疹子了 Lime Disease: How a Fruity Drink Can Give You a Rash

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Picture this: you're on a beach, relaxing, sipping on a beer. You squeeze a lime into your drink and get hit by some citrusy mist while you're sunbathing.

No big deal, right? Well, actually, because of some chemicals in that lime and UV radiation from the sun, your skin is about to get attacked.

The symptoms come a day or two after exposure: an itchy, burning rash with fluid-filled blisterskind of like a bad sunburn. It's been called lime diseasethat's "lime" with an "i".

You might also hear it called Mexican beer dermatitis, margarita dermatitis, or Club Med dermatitis, after the tourism company because sometimes people come back with post-vacation rashes. The medical name for this condition is phytophotodermatitis, which tells us that it's skin damage related to plants and light.

Specifically, high-energy ultraviolet light, like the UV rays in sunlight. This bad skin reaction is caused by certain furanocoumarins, a group of compounds that some plants use to defend themselves and deter hungry herbivores.

They're in some common plants like celery, parsley, parsnip, and some citrus fruits like lemons and limes. Furanocoumarins aren't toxic cell-damaging chemicals on their own.

They're activated when they're exposed to sunlight after a plant's cells are broken open. With the energy from the UV radiation in sunlight, furanocoumarins can undergo a chemical reaction and bind to certain bits of DNA inside another creature's cells, messing with the DNA's structure.

When this DNA damage happens, cells can stop working properly and sometimes get killed off. This reaction is designed to stop animals and insects from eating the plant, since a toxic substance doesn't lend itself to a great "mouth feel".

Some animals learn to avoid these toxic plants, but certain creatures have evolved ways to get at their tasty nutrients. Some caterpillar species, for instance, get around this defense by changing their behavior.

They roll up their leaf of choice and munch on the inside. That way, they keep their furanocoumarin-riddled food in the dark, so UV light doesn't activate these toxic compounds.

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