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.
"You can't live in a glass house," he said. "You can't be neurotic, but provoking the gods is not a good thing to do."
Giving foods like nuts, dairy products and fish to young children is also controversial.
"We don't understand food allergies as well as we understand inhalation allergies," Bonagura said.
Many children, according to Bonagura, grow out of an allergic response to milk or eggs by age 5. Peanut and shellfish are more problematic, however, and can cause lifelong allergies.
Peanuts and milk are commonly associated with childhood allergies, but boiling these foods may remove their allergic potential. A recent study finds that boiled peanuts don't cause the allergic response that is caused by dry-roasted peanuts -- the type found in peanut butter.
Medical researchers now believe immunoglobulin E (Ig E), the immune system antibody that causes the body's response to allergens, may not recognize the proteins in peanuts or milk after the foods are boiled.
"If you can denature [damage] the protein that causes the Ig E response, it's unlikely to trigger an allergic response," Bonagura said.
Even with all the debate about preventing childhood allergies, some consensus emerges that can give parents the advice they're looking for to keep their kids healthy and safe. Nelson and other experts point to the recommendations provided by the American Academy of Allergy, Asthma and Immunology for introducing new food to your child.
Solid food, including fruit, vegetables and meat, should be introduced only after six months. After a year, dairy products like milk, yogurt and cheese can be given. Eggs, according to the academy, may be safely given to the child after two years, but nuts and fish should be given only after the child is at least 3 years old.
There is one allergy-causing factor that causes no dissent among experts: smoking.
"The one that nobody questions is exposure to passive smoking, both in-utero [from the mother smoking] and after birth," Nelson said.
"You certainly need to add tobacco smoke as a pollutant contributing to asthma," said William Fisk, senior scientist and head of the Indoor Environment Department at Lawrence Berkeley Laboratories in Livermore, Calif. "It's a very important pollutant, and it has been linked to a number of health effects."
Besides avoiding smoking around children, Fisk has additional advice for parents. Leaving pets outdoors and fixing water leaks will help alleviate pet dander and mold. Keeping a home free of cockroaches and rodents is also important, though this may be difficult in poor, inner-city neighborhoods.
"Technically, there's a lot we can do here, but socially there's not a lot we can do, especially when there's poverty present," Fisk said.