Boys have a higher chance of developing childhood asthma than girls, but they are also more likely to grow out of it, a new study said.

A team from Brigham and Women's Hospital studied more than 1,000 children with asthma for an average of more than eight years. Each year, the children were given breathing tests to measure how much their airways responded to a substance called methacholine, which can trigger asthma.

The girls' reactions did not change over the years, but boys gained tolerance. Researchers said by age 16, they had to double the dose to provoke a reaction in the boys.

By age 18, 14 percent of girls lost their sensitivity, a good sign. But 27 percent of the boys seemed to have outgrown it.

The leader of the study said it was interesting that the gender differences seemed to come into play as patients were entering puberty.

The results appeared in the second issue for August of the American Journal of Respiratory and Critical Care Medicine.