Christina Desforges, 15, from Saguenay, Canada, went into anaphylactic shock. She was given an adrenalin shot and taken to hospital but died four days later from acute respiratory failure.

Doctors said that a nut allergy brought on by the kiss was the cause of death. The boy, who has not been named, had minute traces of peanut on his lips.

"If peanuts are still in the mouth, or on the tongue or on the lips, they can cause a reaction," said Dr Karen Sigman, an allergy expert. "Teenagers with allergies have to let their friends know. If they are going to be dating somebody, then they have to tell the people they are close to that they are allergic to make sure they are not in contact with nuts or peanuts."

Christina is thought to have suffered a hyper-immune reaction. This causes the body to produce aggravated amounts of antibodies, leading to inflammatory hypersensitivity.

Peanut allergies are widespread but seldom fatal. The symptoms can include hives, plunging blood pressure and swelling of the face and throat, which can inhibit breathing.

About 1.5 million Americans are severely allergic to the smallest trace of peanuts and about 100 people a year die of food allergies