NEW YORK — Parents are reporting more skin and food allergies in their children, a big government survey found.
Experts aren’t sure what’s behind the increase. Could it be that children are growing up in households so clean that it leaves them more sensitive to things that can trigger allergies? Or are mom and dad paying closer attention to rashes and reactions, and more likely to call it an allergy?
‘‘We don’t really have the answer,’’ said Dr. Lara Akinbami of the Centers for Disease Control and Prevention, the senior author of the new report released Thursday.
The CDC survey suggests that about 1 in 20 US children have food allergies. That’s a 50 percent increase from the late 1990s. For eczema and other skin allergies, it’s 1 in 8 children, an increase of 69 percent. It found no increase, however, in hay fever or other respiratory allergies.
Already familiar with the trend in food allergies are school nurses, who have grown busier with allergy-related duties, like banishing peanuts at school parties or stocking emergency allergy medicine.
Sally Schoessler started as school nurse in 1992 in New York state, and didn’t encounter a child with a food allergy for a few years. But by the time she left school nursing in 2005, ‘‘there were children in the majority of classrooms’’ with the disorder, said Schoessler, who now works at the National Association of School Nurses in Silver Spring, Md.
Food allergies tend to be most feared; severe cases may cause anaphylactic shock or even death from eating, say, a peanut. But many food allergies are milder and something children grow out of. Skin conditions like eczema, too, can be mild and temporary.
It’s been difficult getting exact numbers for children’s allergies, and the new report isn’t precise. It uses annual surveys of thousands of adults interviewed in person. The report compares answers from 1997-99 with those from 2009-11.
Parents were asked whether in the previous year their child had any kind of food or digestive allergy, any eczema or skin allergy, or any kind of respiratory allergy like hay fever.
The researchers did not ask if a doctor had made the diagnosis or check medical records. So some parents may have been stating a personal opinion, and not necessarily a correct one.
‘‘We see a lot of kids in clinic that really aren’t’’ allergic to the foods their parents worry about, said Dr. Morton Galina, a pediatric allergist at Atlanta’s Emory School of Medicine.
For example, hives are sometimes blamed on a certain food when a virus was the actual cause, he added.
But experts also said they believe there is a real — and unexplained — increase going on, too.
One of the more popular theories is ‘‘the hygiene hypothesis,’’ which says that exposure to germs and parasites in early childhood somehow prevents the body from developing certain allergies.
The hypothesis argues that there is a downside to America’s culture of disinfection and overuse of antibiotics. The argument has been bolstered by a range of laboratory and observational studies, including some that have found lower rates of eczema and food allergies in foreign-born children in the United States.
There could be other explanations, though. Big cities have higher childhood allergy rates, so maybe some air pollutant is the unrecognized trigger, said Dr. Peter Lio, a Northwestern University pediatric dermatologist who specializes in eczema.
Some suspect the change has something to do with the evolution in how foods are grown and produced. But Lio said tests haven’t supported that.