feed if their children were born in Mexico. While children born in the United States may be more likely to receive regular healthcare, and therefore more likely to be diagnosed with asthma, the researchers said the higher U.S. asthma rates held even when they took this into account. No one knows what causes asthma, which is marked by sometimes serious episodes of wheezing. One theory is the so-called hygiene hypothesis, which suggests that children not exposed to certain allergens early in life are more likely to develop asthma and allergies. Other research shows that specific types of air pollution may make asthma more common, while longer time breast-feeding may reduce the risk. --SP 2343 Local Time 2043 GMT
