I came across this article a few days ago. The comments are hilarious, including several links to medical articles stating exactly what M'Sharak
I knew a child who takes regular medication because simply being around oak trees at certain times of the year could trigger anaphylactic shock (this was several years ago and I can't remember exactly what triggers the allergy, only that she was "allergic to oak trees"). The child's mother, a nurse, made sure the child always took her medication, always had an epi-pen on her, and sent the child on her merry way outside to play with the other children. No way in hell did she expect a single tree that wasn't on her own property to be cut down, even though in this rare case being around an oak tree really could kill her child. The child was four years old when the allergy suddenly developed, and from that age she could recognise an oak tree and knew to stay away from it.