About 150 million people worldwide have asthma. In the United States, it affects more than 20 million people, including 9 million children.

Certain people are at a greater risk for developing the disease:

• Those who live in the inner city. Overall, 8.8 percent of blacks have asthma, compared with about 7 percent of whites. But when they live in the inner city, African-Americans are twice as likely as whites to die from the disease and three times more likely to be hospitalized by it. Meanwhile, the nation's highest rate of asthma is among children of Puerto Rican descent living in New York City.
• Having a parent with asthma gives you a one in four chance of developing the disorder. If both your parents are affected, the odds are one in two that you'll also be asthmatic. You also can inherit atopy, a tendency to develop the allergies that underlie many cases of asthma in children. But this doesn't mean that you will be allergic to the same things as your parents. For example, if your mother has hay fever, you might be allergic to animal dander.
• Living with a smoker boosts your odds of being asthmatic. Between 20 and 25 percent of all cases of childhood asthma are linked to at least one parent who smokes. A child whose mother smokes at least a half-pack a day, is twice as likely to develop asthma as a child of a nonsmoker. Being born premature may result in lung damage that makes you more susceptible to developing asthma.
• Having allergies such as hay fever, food allergies or eczema at a very young age — typically before age 3 — is another risk factor. The same is true for children who have a severe viral infection during infancy such as bronchiolitis, an inflammation of the smallest airways that typically occurs in children younger than age 2.

Meanwhile, asthma causes approximately 4,200 deaths and 500,000 hospitalizations each year.

Factors that put you at risk of dying from asthma include living in the inner city; being hospitalized for emergency asthma treatment at least twice in the past year; having large, daily variations in peak-flow measurements prior to an attack; and having a history of psychiatric disease, depression, alcohol abuse, recent unemployment or extreme denial or anxiety following an attack.