No one has figured out a fool-proof way to prevent asthma. Researchers do have some theories about what might help reduce a child's risk of developing the condition. These include the following:

There is some evidence that limiting your infant's or young child's exposure to common allergens and irritants could help prevent asthma. These include tobacco smoke, dust mites, pet hair, cockroaches, and pollen.

Some evidence also suggests that exposing newborns to other children early in life can help protect against asthma. The reason: It helps build up their immune system.

In one study, newborns who had siblings or who were in day care during their first six months of life had more wheezing episodes up to age 2. But they had significantly lower incidence of both asthma and allergies later in childhood.

Experts suspect that other factors may reduce the risk of asthma as well:

• Breastfeeding. Some studies show that breastfeeding for at least four months may help protect a child against asthma. But other studies fail to back this up.
• A healthy weight. Children who are obese are more likely to develop asthma than children who maintain a healthy weight.
• Diet. Some scientists think that children who don't eat enough vitamin E, calcium, magnesium, potassium, and other nutrients may be at greater risk for asthma. Other studies found that eating fresh fruit and fish may keep children's lungs healthy.