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The number of children with asthma has rocketed in recent years and continues to rise.

About 1 in 7 children in the United States get asthma at some point in their childhood.¹ Many of these will grow out of it. About 1 in 10 children have asthma at any one time.

Asthma is getting more common. About 3 in 10 children had asthma in 1980. This compared with over 5 in 10 during the mid 1990s.² Boys are more likely to get asthma than girls.

It is not clear why more children are getting asthma today than in the past.³ People used to blame an increase in air pollution for the rise in childhood asthma. But this seems unlikely, as many of the most polluted countries in the world, such as China and Eastern European countries, have low rates of asthma.⁴

One of the most popular explanations at the moment for the increase in asthma is the "hygiene hypothesis." This blames increasing asthma rates on cleaner homes, which means that children get fewer infections than they used to. Some scientists think that childhood infections help to build up the immune system. So, since children are getting fewer infections, they have less protection against asthma.⁵

Another idea is that central heating and having more soft furnishings in homes have allowed house dust mites to multiply. (Dust mite droppings are one of the main allergens that trigger asthma attacks.)

Here are some facts about asthma in children.

• Boys are more likely than girls to get asthma. But girls are more likely than boys to have asthma as adults.²
• Up to 75 percent of children with asthma grow out of it in adolescence.⁶
• In many other children, symptoms become less severe as they grow older.⁷