If parents feel a bit confused about how to keep their children safe from allergies and asthma, it's no wonder: Even the experts disagree on the subject.
Are allergies inherited from parents, as some researchers claim? Or is it a child's environment that causes the sneezing, coughing, wheezing and other misery that allergies and asthma bring?
Some parents wonder whether they should expose their kids to potential allergens at an early age to ward off allergies and asthma. Or is it a better idea to keep a child away from pets, pollen, smoke, and foods like nuts and fish?
Though doctors continue to debate these issues, the latest research offers clear, common-sense advice for avoiding or minimizing childhood allergies.
A growing body of research supports the "hygiene hypothesis," which is the theory that early childhood exposure to animals, plants and other allergens will prevent or minimize allergies and asthma. So, an overly hygienic environment, like an immaculate home and a minimum of outdoor activity, may lead to more allergies, proponents claim.
"The idea is that a child's immune system shortly after birth needs a little help to get it started in the right direction," said Harold Nelson, an allergist and professor of medicine at the National Jewish Medical and Research Center in Denver.
"It is the dominant hypothesis at this time, and there's a huge amount of data that supports this," Nelson added.
Nelson cited recent research that found a 50-fold increase in the incidence of allergies and asthma among children growing up in more affluent urban areas over children living in native villages in Africa.
Other research from Europe finds children living in rural and farming communities who grow up surrounded by animals, plants, and other potential allergens have fewer allergies than city-dwelling kids.
But does this mean genetics and a family history of allergies count for nothing?
"Genetics are huge," Nelson said. "But given the choice between the two, the environmental influence is greater than the genetic in epidemiological studies."
"It isn't that simple," said Vincent Bonagura, professor of pediatrics, microbiology and immunology at the Albert Einstein College of Medicine in New York. "Genetics is terribly important."
"It [hygiene] has a role, but it's not as simple on a global level as people like to make it," Bonagura said.
Bonagura explained, "If you look at New York City in the inner city, where you have children being raised with multiple siblings and exposed to many allergens, you'd expect to see evidence to support the hygiene hypothesis, but the incidence of asthma is increasing."
Environmental allergies aren't restricted to a single source, Bonagura notes. "People who tend to have an allergic response, and move to a new environment, three or four years later develop a reaction to new allergens," he said.
When there is a family history of allergies or asthma, Bonagura advises parents to use practical measures to avoid or minimize allergies.
"You have to be diligent about what you give to the child," he said. If there's a family history of pet allergies, for example, "You don't need to have a dog or a cat in the house."
Bonagura also recommends a dose of common sense when keeping kids away from allergens.