Answer: Limes

Every summer, ER doctors across America see patients with horrible blistering and swelling on their hands. The patients are almost always bewildered and have no idea how their hands ended up in such a state, but the culprit is often revealed to be limes (sometimes lemons).

How do the patients end up going from a fun afternoon of margaritas to agonizing blisters all over their hands? They’re suffering from phytophotodermatitis, a relatively rare condition wherein photosensitizing compounds in plants end up on the skin and then the skin is exposed to sunlight (ultraviolet light) for an extended period of time. The result is horrific blistering sunburns that take weeks to heal up.

While there are more than a few plants that contain these photosensitizing compounds—like parsnips, carrots, and figs—the preparation methods we use to cook and eat these foods don’t include getting the juices and oils from them all over our hands. Limes and lemons, however, we juice for party drinks (where we’re outside in the sun). Washing our hands after getting, say, liquid from the raw chicken we’re putting on the grill is second nature, but how many people think it particularly pressing to go wash a little bit of lime juice off the back of their hands?

If a big party with a lot of citrus-based cocktails is on your summer to-do list, however, do take some precautions: juice the lemons and limes inside, wash your hands well to get the juice and oils off, and play it extra safe by applying sunscreen to your hands afterwards. No margaritas, no matter how delicious, are worth the agony of weeks of blistering and cracking.