A US government report revealed that children's allergies are on the rise in the United States and are particularly common among the wealthiest in society.
Skin allergies such as eczema have risen the most over the past decade, going from a prevalence of 7.4 percent in 1997-1999 to 12.5 percent in 2009-2011, said the report by the National Center for Health Statistics on children up to age 17.
Food allergies also rose from 3.4 percent to 5.1 percent over that time span.
Rates of respiratory allergy, such as hay fever, stayed about the same and continued to be the most common childhood allergy (17 percent).
Allergies are the body's way of over-reacting to substances that the immune system should find harmless, such as pollen, milk or peanuts.
Some experts believe the rising rates of allergies in the United States and other parts of the developed world are a result of increasing hygiene, eliminating microbes that would otherwise help children develop defenses to bacteria and viruses.
The NCHS study, based on answers from the National Health Interview Survey, found that Hispanic children in the United States had a lower rate of all kinds of allergies compared to other groups.
They also found that the prevalence of food and respiratory allergy increased with income.
"Children with family income equal to or greater than 200 percent of the poverty level had the highest prevalence rates," it said.
Among children below the poverty line, 4.4 percent had a food allergy and 14.9 had a respiratory allergy.
In families with the highest incomes, 5.4 percent had a food allergy and 18.3 percent had a respiratory allergy. There was no significant difference in skin allergies across income lines.