When a leukemia patient received a bone marrow transplant from his sister, all went smoothly—until he bit into a kiwi fruit and his lips began to tingle and swell.

Turns out the patient was suffering from the "oral allergic symptom" his sister had long endured, and now that her bone marrow cells were in his body, he is to share in that suffering possibly for the rest of his life, reports ScienceAlert.

This kind of allergy transfer has been observed in bone marrow transplant patients before, but researchers reporting in the Journal of the European Academy of Dermatology and Venereology say this is the first time that such an allergy transfer has actually been proven, a finding that could help scientists better understand how allergies start in the first place and thus how to treat them.

An allergic reaction is typically the body's immune system mistaking something that is harmless, such as an otherwise safe type of food or dust, for something it needs to fight.

The blood cells themselves are behind this reaction, and because most blood cells form in our bone marrow, this type of transplant may actually result in a semi-permanent or permanent allergy transfer.

And while it's extremely rare, other procedures have been shown to at least temporarily transfer allergies between patients, as was the 2015 case in which an 8-year-old Canadian boy developed a severe allergy to fish and peanuts following a blood transfusion, reports RedOrbit.

In the kiwi case, scientists used fluorescence in situ hybridization (FISH) to prove that the cells causing the man's allergy had indeed come from his sister.

(Women seem to suffer from more severe allergic reactions.)

This article originally appeared on Newser: Man Inherits Sister's Kiwi Allergy in Most Unusual Way

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