Bacteria are generally thought of as causing disease, but one germ living in the stomach might keep some children from developing asthma or other allergies.

Doctors associated with New York University studied H. pylori bacterium, commonly found in the human stomachs. The results of their study showed that the bug can increase the risk of stomach ulcers but might be beneficial in other ways.

"Children that had H. pylori were much less likely to develop asthma, hay fever and eczema and other allergic conditions," Dr. Martin Blaser, with NYU's Langone Medical Center, said.

Children with the stomach bacteria were 30 to 60 percent less likely to develop asthma. The exact cause of that reduced risk, though, remains unclear, doctors say.

"If we can understand the mechanism of how that worked, maybe it will help us to prevent asthma," Dr. Yu Chen, with the NYU School of Medicine, said.

In recent decades, H. pylori has been disappearing from the American population. Doctors think one cause might be that antibiotic use has dramatically increased.

"At the same time H. pylori is going down, asthma is going up," Blaser said.

Blaser said he believes that microbe might hold the key to future asthma and allergy treatments.

"Maybe we'll find a milder form of H. pylori that we can give to kids that will give us the benefits without giving us the risk" – and perhaps lowering asthma rates among children, Blaser said.