As allergies rise, so does knowledge of causes
Medical thinking on children’s allergies is undergoing huge changes as scientists begin to understand their underlying genetic and molecular causes. Where parents were once told there wasn’t much they could do to avoid allergies, researchers are beginning to home in on how they can be prevented.
USA TODAY reporter Elizabeth Weise posed questions to a panel of experts on the problem.
Question: What are allergies?
Answer: They’re an abnormal response by the immune system to things the body should perceive as harmless. The body makes an antibody called IgE that sticks to dangerous foreign substances such as viruses, bacteria and toxins so white blood cells can find and destroy them, Hugh Sampson says.
Children who are genetically predisposed to allergies have a kind of “hair-trigger” immune response in which the antibody adheres to substances that aren’t really a threat, such as foods, pollen, dust and animal dander. The subsequent attack causes the inflammatory reaction that is the hallmark of allergic reaction, Sampson says.
Q: What causes allergies in children?
A: It requires genetics, environment and exposure.
First they must be genetically predisposed to an allergy.
Then they’ve got to be exposed to the allergen.
And doctors now believe that there are certain environmental factors that make it more or less likely that they’ll develop an allergy, Josi Saavedra says.
Q: What environmental effects have been found?
A: One study done in Los Angeles found a link between diesel particles in the air and asthma rates. And numerous studies have found a direct link between living with a smoker and higher allergy rates of all kinds, Sampson says.
Q: Are allergies among children increasing?
A: Forty million to 45 million Americans – 15 percent to 20 percent of the population – have some type of allergy, most of which surface during infancy or childhood, according to the American College of Asthma, Allergy and Immunology.
The “allergic march” is a progression of symptoms that tend to occur in children.
The first is atopic dermatitis, or scaly, itchy skin. Seventy-five percent of children who have atopic dermatitis go on to develop allergic rhinitis or hay fever, and 50 percent of children with hay fever go on to develop asthma, says Saavedra.
Food allergies also are increasing in children, Sampson says: “We now estimate that food allergies affect 3.5 percent to 4 percent of the U.S. population. In the 1980s we were hesitant to say it was 0.5 percent.”
Sampson and colleagues at Mount Sinai School of Medicine in New York studied the prevalence of peanut allergies in the United States and found that in 1997, 0.6 percent of the U.S. population had peanut allergies, which equaled about 1.5 million people. In 2002, researchers found that the prevalence of peanut allergies had doubled.
Scientists don’t know why.
Q: What about the idea that modern life is too “clean” and that itself causes allergies?
A: It’s called the Hygiene Hypothesis. Scientists think that as babies are exposed to less disease, dirt and bacteria, their regulatory immune systems aren’t activating correctly. In effect, without something real to fight, their immune system goes crazy, attacking things that aren’t really dangerous, things like dust, peanuts and wheat, or even itself, which can lead to autoimmune diseases such as type 1 diabetes, William Klish says.
One study in Germany right after unification found that children in the former East Germany had many fewer allergies than those in the former West Germany. Children in East Germany went into day care centers at very young ages, where they proceeded to give each other lots of colds.
Having the diseases protected them against allergies, von Berg says, because their immune systems had something real to fight.
Protecting children
• Breast-feed for at least the first four to six months of a child’s life to help prevent allergies, von Berg says.
• Don’t smoke. There’s universal agreement and numerous studies that being exposed to secondhand smoke increases asthma rates, Klish says.
• Don’t be afraid to expose your children to other children. The constant runny nose and colds of the day-care center are actually a good substitute for the passel of children that most families used to have, Sampson says.
Researchers now say that exposure to the common illnesses of childhood helps fine-tune a child’s immune system. Without such exposure, it sometimes strikes out at the wrong things, causing allergies and autoimmune disorders.
• Don’t have peanuts or products containing peanuts in the house until your child is at least 1. Children can be sensitized to peanuts simply by having someone else in the house eat them.
A British study found that families with peanuts in the house have a higher rate of peanut allergy compared with households with no peanut exposure, Sampson says.
But the jury’s out on whether pregnant women should avoid peanuts. Some researchers say prenatal exposure can trigger sensitivity; others say it can protect the child.
• If you’re going to have dogs and cats, get them before you have children. Research has shown that when there already is a dog or a cat in the house when a baby arrives, the child gains some protection against later developing animal allergies, Saavedra says. Dogs appear to be slightly more protective than cats.
But getting a pet even a few months later doesn’t have the same effect, Saavedra says. And all doctors agree that if the child shows any signs of sensitivity, the animals should be removed from the house.
• Get some cows and pigs and take the baby to work. OK, we’re not being serious here. But researchers have found that in cultures in which mothers work in the stables with cows and pigs when they’re pregnant and then bring their babies in with them while they work, children have almost no asthma, von Berg says.