New Delhi, Oct 26 (IANS): Women exposed to smoke from burning wood and related "biomass" combustibles, such as leaves, crop stalks, and dung are more likely to suffer from respiratory problems including chronic obstructive pulmonary disorder (COPD).

It could be because men were found to have significantly higher markers of an inflammatory response in cells that line the nasal passages relative to men exposed to filtered air.

By contrast, for women, the wood smoke exposure appeared to lower markers of the inflammatory response.

While the scientists are not yet sure about the difference in the sex-specific responses, one theory suggests that evolution may be blamed.

Over thousands of years, women might have had greater and more chronic exposure to smoke from cooking fires compared to men.

"We wonder if a greater wood smoke exposure has led to evolutionary pressure on women to have a more blunted inflammatory response, which would probably result in less damage to the airway during respiratory virus infection," said Ilona Jaspers, Professor at the University of North Carolina.

Other factors include differences in male and female hormone profiles and genetics.

In the study, published in the American Journal of Respiratory and Critical Care Medicine, the team exposed men and women volunteers to wood smoke or filtered air. They then injected them with a standard dose of the live-attenuated influenza virus vaccine which causes a natural yet mild immune response in the nasal passages.

The combined analysis showed the false impression that the wood smoke had almost no effect on the immune response to the live-attenuated influenza virus vaccine.

The study suggests that any research on environmental exposures should take potential sex differences into account as impacts of environmental toxins may be missed when researchers fail to compare effects on men and women.