A 15-year-old Canadian girl with a peanut allergy died after kissing her boyfriend who had eaten a peanut butter sandwich hours earlier, reports say.
Some people are severely allergic to even the smallest peanut traces
Christina Desforges, of Saguenay, Quebec, died last week after she failed to respond to days of treatment.
She had been given an adrenaline shot, a standard treatment for anaphylactic shock, almost immediately after she suffered a reaction.
A peanut allergist in Montreal said the case is "very rare and worrisome".
Ms Desforges' 16-year-old boyfriend had kissed her some nine hours after he had eaten peanut butter on toast, the AFP news agency reported.
"She was extremely allergic to peanuts and her boyfriend didn't know," a reporter for Canadian broadcaster TVA said.
Ms Desforges was taken to a hospital in Saguenay, about 155 miles (250km) north of Quebec City, where she died.
Hospital officials refused to comment. A post-mortem is due to be carried out.
Rhoda Kagan, a peanut allergist at Montreal's Children's Hospital, said some people have an "extremely low threshold" of resistance to peanuts and their traces.
"This varies greatly from person to person and is highly unpredictable," she was quoted by the Associated Press as saying.
Peanut allergy symptoms can include hives, a drop in blood pressure and swelling of the face and throat that can block breathing.