'Fatal Kiss' Puts Spotlight on Food Allergies

French Canadian newspapers are calling it "Un Baiser Fatal" -- a fatal kiss.

Moments after Canadian teen Christina Deforges kissed her boyfriend, she went into shock. She was rushed to a hospital, where she died four days later. She was allergic to peanuts, and her boyfriend had eaten a peanut butter sandwich hours before kissing her.

Doctors say the situation is not as far-fetched as it might sound.

"When someone eats a peanut butter sandwich you will often have peanut left in the mouth," said Dr. Hugh Sampson of the Mt. Sinai School of Medicine.

Michelle Risinger, who is allergic to peanuts, once kissed a boy who had just eaten a cookie with trace amounts of peanut.

"My throat closed. It's a tight, tingling sensation. Then my body swells with hives," Risinger said.

Kids Too Clean?

An estimated 1.5 million Americans have peanut allergies, and nowhere are the numbers growing faster than in the United States.

Some researchers say it's because Americans eat more dry roasted peanuts than the boiled or fried peanuts eaten in Asia.

"Roasting brings about a change in the structure of the protein that makes it much more likely to cause an allergic reaction," Sampson said.

Another possible cause: American children today may be too clean for their own good.

Kids need to be exposed to enough germs at an early age to keep their immune systems busy. If not, say some researchers, the immune system can go awry and overreact to certain foods and allergens.

The only way to prevent an allergic reaction from peanuts is to avoid them. But that's not so easy. Peanuts can be found in everything from tomato sauces and chili to popcorn and lollipops.

Parent Liz Forman said she didn't know anyone who had a peanut allergy when she was growing up. Now both of her sons are allergic.

She said the death of Christina Deforges has taught them a lesson. "Be more careful about not only your own consumption of peanuts but your friends and how close you get to them afterwards," Forman said.

ABC News' John McKenzie reported this story for "World News Tonight."