If your baby has a runny nose it may actually be a good thing. It seems that children who get such minor infections may be less likely to develop asthma later on in life.

The findings appear to support the theory that common infections shape the immature immune system in a way that cuts the risk of asthma and allergies later in life.

The airway inflammation that marks asthma is often caused by an abnormal immune reaction to environmental irritants such as pollen, dust and mold. Previous studies have suggested that certain infections early in life may ward off asthma by pushing the developing immune system toward infection-fighting mode. This, the theory goes, may make children's immune systems less likely to overreact to normally benign environmental factors.

The investigators found that repeated "mild infections" -- runny nose or infection with a herpes virus -- were linked to a lower risk of asthma and allergy.

On the other hand, repeated infections of the lower respiratory tract, such as the flu or pneumonia, were associated with a higher asthma risk. This, the researchers report, suggests that children predisposed to asthma may be more vulnerable to such infections.

Over the past 20 years, asthma has become more and more prevalent worldwide. Some experts put part of the blame on the increasingly sterile conditions in which children are growing up. They point out that smaller families, fewer germs, and more antibiotics early in life may be shaping children's immune systems to overreact to normally harmless irritants.

British Medical Journal February 17, 2001; 322: 390-395