In terms of the effort-to-smugness ratio, becoming an organ donor is probably just about the best thing you can do with your time. It’s easy – you can sign up online if you don’t live somewhere with opt-out laws – it’s incredibly convenient, since you’ll be dead by the time the donation actually happens, and you get to waltz around like you’ve saved the lives of up to eight people, because, well, you genuinely might.

But sometimes, in very rare cases, organ donation can have some unintended consequences. And for one patient in 2018, a life-saving lung transplant came with an unexpected price: a brand-new nut allergy.

“Two weeks after the transplant, the patient developed acute respiratory failure immediately after consuming a peanut butter and jelly sandwich,” explains the case report, published in Transplantation Proceedings. “The recipient patient had never had allergies to peanuts or other nuts before her transplant.”

Although the patient, a 53-year-old woman suffering from emphysema, didn’t show the more common allergy symptoms such as a skin rash or stomach ache, doctors realized her breathing difficulties and chest tightness was an allergy after she told them when it started – just after she chowed down on a delicious PB&J.

The thing was, the woman had never had a peanut allergy before. But somebody else had – the 22-year-old man whose left lung had just been transplanted into her chest. As Dr Mazen Odish, one of the doctors who treated the woman, confirmed to LiveScience, the donor had given the woman not just an organ, but his nut allergy as well.

It’s very unusual for food allergies to be spread via organ donation, but it’s not unheard of. In 2016, a 46-year-old man was given a kiwi fruit allergy along with a bone marrow donation from his sister. And in 2003, one liver transplant recipient inherited the very nut allergy that killed the donor.

Despite these examples, though, scientists aren’t quite sure what causes the phenomenon. There are a few factors that make acquiring a food allergy more likely – most are inherited from liver transplants, and children or people with allergies in their family history seem to be more at risk – but generally, individual cases can vary wildly. For instance, while some organ donations from allergy sufferers come with a free dose of dietary restriction, others don’t. Perplexingly, there have even been cases where organs from the same donor will cause allergies in one recipient, but not in others.

After having her new nut allergy confirmed – she tested positive for allergies to peanuts, almonds, cashews, coconuts, and hazelnuts – the patient was advised to steer clear of the offending seeds, drupes, and legumes and issued with an EpiPen in case of emergencies. And since doctors don’t know if the allergy will disappear over time she will likely have to be monitored for some time to see how, or if, her new condition changes.

[H/T: LiveScience]