“Most of the time asthma attacks are triggered by allergies, but there are some people who have asthma without allergies,” says UTMB’s Dr. William Calhoun. “Women have more asthma than men by about a 60-40 ratio, and boys are more likely to have asthma than girls by the same ratio,” says Calhoun. Experts aren't sure why this is. One thing that seems to determine your susceptibility to asthma is smaller lung size, which means airways are narrower so it takes less inflammation to restrict them. Calhoun says women typically have smaller lungs than men. Likewise, because boys develop slower than girls, boys typically have smaller lungs.