Caryl Schivley says her son, Brenton, was always very careful about what he ate -- until last September 1, when he was at a friend's house and took a cookie from a bowl on the kitchen table.

"He took a bite of the cookie and he said to his friend, 'I shouldn't have eaten that,'" said his mother. Severely allergic to peanuts, the 16-year-old from western Massachusetts made the dire mistake of not asking about the ingredients. Within minutes he developed a severe allergic reaction to the cookie, which contained peanuts.

Within an hour, he was dead.

"He should have asked [about the ingredients] but he didn't," Caryl Schivley said.

A new study published in the Journal of Allergy and Clinical Immunology suggests Brenton's case may not be unique. Researchers analyzed 31 allergy deaths, finding most who died from food-related reactions were teenagers or young adults and were away from home when they ate the item that killed them. (Interactive: Living with food allergies)

"We were surprised that so few people had gotten correct information about ingredients in restaurant settings, which accounted for about half of these fatal reactions," said study author Anne Muñoz-Furlong, founder and CEO of the Food Allergy and Anaphylaxis Network, a nonprofit advocacy and education group. "The individuals either did not ask about ingredient information -- and assumed the food was safe -- or the restaurant staff gave them incorrect or incomplete information." (Kids and food allergies )

An estimated 12 million Americans suffer from food allergies, and about 150 die every year.

The new study was conducted by researchers at Furlong's organization, National Jewish Medical and Research Center in Denver, Colorado, and Mount Sinai School of Medicine in New York.

Of those who died after accidentally eating the food to which they were allergic, 58 percent were between the ages of 13 and 30. Of the 31 people the study examined, 68 percent had eaten outside of their home, for example at a restaurant, school cafeteria or the home of friends. More than 80 percent of the deaths were caused by peanuts or tree nuts, such as almonds, cashews and pecans. The study also documented four milk-allergic individuals who died after accidental exposure to a dairy containing product and two who had eaten shrimp.

In a food allergy -- unlike intolerance -- the immune system mistakenly identifies a food as being dangerous and reacts acutely against it.

Experts say those with severe food allergies should always carry self-injectable epinephrine, a form of adrenaline usually carried in a small device called an Epipen, in case of accidental ingestion of an offending food. However, the study found that the majority of those who died did not have epinephrine administered in a timely manner.

After eating the cookie, Brenton took an over-the-counter antihistamine but that didn't help. His mother said the Epipen that Brenton normally carried in his backpack was not with him.

Knowing he was in danger, Brenton called his mom. She raced to him with his injectable epinephrine within four minutes, but she estimates at least half an hour had elapsed since he had eaten the cookie. He had collapsed on the sidewalk by the time she was able to administer the epinephrine. "We called the ambulance and they could never revive him," his mom said.

The "sooner these reactions can be treated with epinephrine, the more likely you are to have a good outcome," said Dr. Hugh Sampson, director of the Jaffe Food Allergy Institute at New York's Mount Sinai School of Medicine, and a study co-author.

Sampson likens an allergic reaction to a "snowball coming down a mountain." At the top of mountain it's small "but by the time it gets to the bottom of the mountain it becomes huge."

For those with food allergies, vigilance about food preparation is essential to staying safe. "The extra challenge for teens with food allergies is that they need to be careful about every food that goes into their mouth or into the mouth of someone they're going to kiss and yet the driving force for teens is to be like everyone else and to be very social," Muñoz-Furlong said. "When they're younger, parents are more involved" in their children's daily activities, says Brenton's mother, Caryl Schivley. But as teenagers, "they don't want to make a spectacle of themselves."

Most of those who died that the new study documented had asthma in addition to their food allergy.

The study found that many who died had not needed prescribed medication for previous reactions. Some did not even know that food-induced allergic reactions could be fatal.

The research team in 2001 reported on a previous group of 32 individuals who had died because of food-induced anaphylaxis, and reviewed medical literature in the United States and internationally in order to try to determine the similarities or differences in the factors that led to the fatalities.

"What was most heartbreaking," said Muñoz-Furlong, "is that the story repeats itself over and over again and the fact that these deaths are preventable."