Scientists say they may have found a sort of magic ingredient to prevent asthma in children: microbes from farm animals, carried into the home in dust.
The results of their research, published on Wednesday in The New England Journal of Medicine, were so convincing that they raised the possibility of developing a spray to do the same thing for children who do not have regular contact with cows and horses.
It is a pressing problem because as many as 10.6 percent of grade-school children have asthma, according to data from the Centers for Disease Control and Prevention. And there is no cure for this chronic and frightening disease.
The discovery originated with an idea that has been around for years: that a growing number of children were developing asthma because their daily environments were simply too clean.
If children are exposed to microbes that stimulate their immune systems in the first few years of life, they will be protected against asthma, the hypothesis says. As asthma rates climbed, researchers published study after study supporting what has become known as the hygiene hypothesis.
The most consistent findings were from studies that compared children who grew up on farms — less asthma — with children who grew up in other environments.
But in every case, there were many other differences between the children who had less asthma and those who had more. So it was not clear what exactly might have led to different asthma rates.
What was missing was evidence that one essential factor in the environment was protecting children. And what was needed was a reason it had exerted its effect. The new study provides this, asthma researchers say, which is what makes its results so spectacular.