ATLANTA — Food allergies in American children seem to be on the rise, now affecting about 3 million kids, according to the first federal study of the problem.

But experts said that might be because parents are more aware and quicker to have their kids checked out by a doctor.

About 1 in 26 children had food allergies last year, the Centers for Disease Control and Prevention reported today. That’s up from 1 in 29 kids in 1997.

The 18 percent increase is significant enough to be considered more than a statistical blip, said Amy Branum of the CDC, the study’s lead author.

Nobody knows for sure what’s driving the increase. A doubling in peanut allergies — noted in earlier studies — is one factor, some experts said. Also, children seems to be taking longer to outgrow milk and egg allergies than they did in decades past.

But also figuring into the equation are parents and doctors who are more likely to consider food as the trigger for symptoms like vomiting, skin rashes and breathing problems.

“A couple of decades ago, it was not uncommon to have kids sick all the time and we just said ‘They have a weak stomach’ or ‘They’re sickly,”’ said Anne Munoz-Furlong, chief executive of the Food Allergy & Anaphylaxis Network, a Virginia-based advocacy organization.

Parents today are quicker to take their kids to specialists to check out the possibility of food allergies, said Munoz-Furlong, who founded the nonprofit in 1991.

The CDC results came from an in-person, door-to-door survey in 2007 of the households of 9,500 U.S. children under age 18.

When asked if a child in the house had any kind of food allergy in the previous 12 months, about 4 percent said yes. The parents were not asked if a doctor had made the diagnosis, and no medical records were checked. Some parents may not know the difference between immune system-based food allergies and digestive disorders like lactose intolerance, so it’s possible the study’s findings are a bit off, Branum said.

However, the study’s results mirror older national estimates that were extrapolated from smaller, more intensive studies, said Dr. Hugh Sampson, a food allergy researcher at the Mount Sinai School of medicine.

“This tells us those earlier extrapolations were fairly close,” Sampson said.

The CDC study did not give a breakdown of which foods were to blame for the allergies. Other research suggests that about 1 in 40 Americans will have a milk allergy at some point in their lives, and 1 in 50 percent will be allergic to eggs. Most people outgrow these allergies in childhood.

About 1 in 50 are allergic to shellfish and nearly 1 in 100 react to peanuts, allergies that generally persist for a lifetime, according to Sampson.

Some people have more than one food allergy, he said, explaining why the overall food allergy prevalence is about 4 percent.

Children with food allergies also were more likely to have asthma, eczema and respiratory problems than kids without food allergies, the CDC study found, confirming previous research.

The study also found that the number of children hospitalized for food allergies was up. The number of hospital discharges jumped from about 2,600 a year in the late 1990s to more than 9,500 annually in recent years, the CDC results showed.

Also, Hispanic children had lower rates of food allergies than white or black children — the first such racial/ethnic breakdown in a national study.

The reason for that last finding may not be genetics, said Munoz-Furlong. She is Hispanic and said people in her own family have been unwilling to consider food allergies as the reason for children’s illnesses. “It’s a question of awareness,” she said.

On the Net:

The CDC report: http://www.cdc.gov/nchs