Dec. 26 (HealthDay News) -- Childhood milk and egg allergies may be more persistent and harder to outgrow than they were a generation ago, U.S. researchers report.

In two studies from the Johns Hopkins Children's Center, researchers followed more than 800 youngsters with milk allergy and almost 900 youngsters with egg allergy for more than 13 years.

They found that the allergies often persist well into the school years and beyond.

Earlier research suggested that about 75 percent of children with milk allergy outgrew the allergy by age 3. But the Hopkins researchers found that only 20 percent of children with milk allergy outgrew it by age 4, and 42 percent outgrew it by age 8. By age 16, 79 percent no longer had the allergy.

There were similar findings among the children with egg allergy. Only 4 percent outgrew it by age 4, 37 percent by age 10, and 68 percent by age 16.

The studies were published in the November and December issues of the Journal of Allergy and Clinical Immunology.

"The bad news is that the prognosis for a child with a milk or egg allergy appears to be worse than it was 20 years ago," lead investigator Dr. Robert Wood, head of allergy and immunology at Hopkins Children's, said in a prepared statement. "Not only do more kids have allergies, but fewer of them outgrow their allergies, and those who do, do so later than before."

The findings seem to confirm what many pediatricians have long suspected -- that food allergies diagnosed in recent years behave more unpredictably and aggressively than food allergies in the past.

"We may be dealing with a different disease process than we did 20 years ago. Why this is happening we just don't know," Wood said.

SOURCE: Johns Hopkins Children's Center, news release, Dec. 12, 2007