WASHINGTON — Elizabeth White’s first encounter with peanuts — a nibble of a peanut butter cracker at age 14 months — left the toddler gasping for breath. Within minutes, her airways were swelling shut.A mere fifth of a peanut was enough to trigger an allergic reaction. So it was with trepidation that her parents enrolled Elizabeth, at 4[1/2], in a groundbreaking experiment: Could eating tiny amounts of the very foods that endanger them eventually train children’s bodies to overcome severe food allergies?

It just may work, suggest preliminary results from a handful of youngsters allergic to peanuts or eggs — and who, after two years of treatment, seem protected enough that an accidental bite of the forbidden foods is no longer a huge threat.

“We’re so lucky,” says Carrie White, Elizabeth’s mother.

Now seven, Elizabeth can safely tolerate the equivalent of seven peanuts. For the first time, the Raleigh, North Carolina, girl is allowed to go on play dates and to birthday parties without her parents first teaching the chaperones to use an EpiPen, a shot of epinephrine that can reverse a life-threatening reaction.

Don’t try this experiment on your own, warns lead researcher Dr. A. Wesley Burks of Duke University Medical Center. Children in the study are closely monitored for the real risk of life-threatening reactions.

But if the work pans out — and larger studies are beginning — it would be a major advance in the quest to at least reduce severe food allergies that trigger 30,000 emergency-room visits and kill 150 people a year.

“I really think in five years there’s going to be a treatment available for kids with food allergy,” says Burks.

Millions of Americans suffer some degree of food allergy, including 1.5 million with peanut allergy, considered the most dangerous type. Even a whiff of the legume is enough to trigger a reaction in some patients.

Moreover, food allergies appear to be on the rise. Peanut allergy in particular is thought to have doubled among young children over the past decade, prompting schools to set up peanut-free cafeteria zones or ban peanut-containing products.

There’s no way to avoid a reaction other than avoiding the food, something the new research aims to change.

Allergies to pollen and other environmental triggers often are treated with shots called immunotherapy.