Exposure to a combination of excess stress hormones and chemicals while in the womb could affect a man's fertility in later life, a study suggests.
Researchers looked at the effect of stress hormones - glucocorticoids - combined with a common chemical used in glues, paints and plastics. They found that the combination strikingly increased the likelihood of reproductive birth defects.
These include cryptorchidism, when the testes fail to drop, and hypospadias, when the urinary tract is wrongly aligned. The conditions are the most common birth defects in male babies.
Researchers from the University of Edinburgh and Medical Research Council believe the findings could help explain why rates of babies born with these problems are increasing.
Dr Mandy Drake, at the University of Edinburgh's Centre for Cardiovascular Science, said: "What the study shows is that it is not simply a case of one factor in isolation contributing to abnormalities in male development but a combination of both lifestyle and environmental factors, which together have a greater impact.
"In most studies reproductive disorders are only seen after abnormally high levels of exposure to chemicals, which most humans are not exposed to. Our study suggests that additional exposure to stress, which is a part of everyday life, may increase the risk of these disorders and could mean that lower levels of chemicals are required to cause adverse affects."