A study published in the American Journal of Respiratory and Critical Care Medicine has found that babies exposed to antibiotics in utero have an increased risk of allergic diseases such as eczema, asthma and hay fever. The prevelence of allergic diseases has increased dramatically in the developed world over the last 50 years. This increase mirrors the increase in antibiotic use, thereby reducing exposure to microbes early in life. Because the immune system develops in utero, factors that modify exposure to microbes may have a long term impact on the risk of developing these allergic diseases. One of these factors is antibiotic exposure.