First peanuts, now eggs. Doctors have reversed allergies in some children and teens by giving them tiny daily doses of problem foods, gradually training their immune systems to accept them.

In the best test, about a dozen youngsters were able to overcome allergies to eggs, one of the most ubiquitous foods, lurking in everything from pasta and veggie burgers to mayonnaise and marshmallows. Some of the same doctors used a similar approach on several children with peanut allergies a few years ago.

Don't try this yourself, though. It takes special products, a year or more and close supervision because severe reactions remain a risk, say doctors involved in the study, published in the new edition of The New England Journal of Medicine.

"This experimental therapy can safely be done only by properly trained physicians," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, the federal agency that sponsored the study.

It didn't work for everyone, and some dropped out of the study because of allergic reactions. But the results "do show there is promise for future treatment" and should be tested in a larger group of youngsters, said the study's leader, Dr. A. Wesley Burks, pediatrics chief at the University of North Carolina, Chapel Hill.

More than 2 percent of young children have egg allergies, suffering wheezing and tight throats or life-threatening reactions if they eat any egg, Burks said. Many will outgrow this by age 4 or 5, and more will by the time they are teens, but 10 to 20 percent never do. The big worry is that these youngsters will eat eggs as an ingredient in a food they don't realize contains them, and have a severe reaction. Training a child's immune system to tolerate even small amounts of egg to prevent this was the goal of the study.

It enrolled 55 children ages 5 to 18. Forty were given tiny daily amounts of powdered egg white, the part that usually causes the allergy. The other 15 were given cornstarch — a dummy treatment — for comparison. The amounts were increased every two weeks until youngsters in the treatment group were eating about one third of an egg each day.

They periodically went to their doctors to try eating eggs. They failed the test if a doctor could see any symptoms, such as wheezing.

At about a year, none receiving the dummy treatment passed the egg challenge. Those on the egg-white powder fared better.

"At the end of the year, half of them passed. At the end of two years, 75 percent of them passed," Burks said.

He went a step further, to see if participants could maintain tolerance without the daily powder. Those who passed the second test stopped using the powder, avoided eggs entirely for four to six weeks, then tried eating eggs again as they wished. Eleven of the 30 youngsters were able to do this with no problem.