(CNN) -- Food and skin allergies are becoming more common in American children, according to a new report from the Centers for Disease Control and Prevention. Both have been steadily increasing for more than a decade.
Food allergy prevalence increased from 3.4% to 5.1% between 1997 and 2011, while skin allergy prevalence more than doubled in the same time period. That means 1 in every 20 children will develop a food allergy and 1 in every 8 children will have a skin allergy. According to the CDC, respiratory allergies are still the most common for children younger than 18.
The new report, which looked at data from the National Health Interview Survey, found that skin allergies decreased with age, while respiratory allergies increased as children got older.
Both food and respiratory allergies also increased with income level, meaning richer families had higher rates of childhood allergies. Hispanic children had lower rates than non-Hispanic white and black children in the survey. The report did not look into the potential reasons for this.
Scientists are still trying to figure out where allergies come from, and why they're on the rise in the United States. Internal bacteria, genetics and environment may all play a role, says Dr. Edward Zoratti, head of the allergy and immunology division at Henry Ford Hospital in Detroit.
Why are food allergies on the rise?
When particles of pollen or certain types of food enter our bodies, they're called antigens. If your body has a sensitivity to that particle, it mistakes the harmless element for a dangerous invader, according to the American Academy of Allergy, Asthma and Immunology. The particle then becomes what we call an allergen.
Allergens cause your body to produce Immunoglobulin E, or IgE, antibodies. Antibodies are used to identify and destroy dangerous invaders. Unfortunately, IgE antibodies also release histamine and other chemicals that can create an allergic reaction.
That means anything that impacts our immune system could change our susceptibility to allergies, Zoratti says. For instance, our diet has changed over time -- "and not for the better" -- with more processed food and fewer natural nutrients. We're also outdoors less and exercise less, all of which may be changing how our immune system reacts to these antigens.
Studies have been done in Europe, he says, that show children who are raised on farms are less likely to have allergies. Researchers believe exposure to animals and various microbes at a young age strengthens the immune system. It's called the "hygiene hypothesis," meaning our body's ability to fight back has been weakened by too clean of an environment.
A lack of vitamin D may also be contributing to the rise in allergies. Many people in the United States have a vitamin D deficiency, Zoratti says. While scientists aren't sure how Vitamin D works, they do know it plays a crucial role in the immune system. There's also a growing concern that the antibiotics we take as children are killing off good bacteria in our gut, making it difficult for the good to fight off the bad.
"There's been a lot of changes in the (microbes) that we're exposed to, or that grow in and on our body," Zoratti says.
Bottom line, scientists are still working to figure out why allergies are on the rise. If your child has an allergy or allergy symptoms, talk to their pediatrician.