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The findings help explain how exposure to substances in the womb might affect offspring down the line. Getty Images


- Inhaling diesel exhaust and mold while pregnant led mice to have offspring that seemed less vulnerable to allergies.

- The study helps connect the dots between exposure to substances in the womb and health later in life.

- There is a lot left to learn before the research can be used to give advice to people.

When pregnant mice inhaled diesel exhaust and mold together, their offspring grew up to have fewer signs of allergies and asthma-like symptoms, found a new study.

The study doesn't imply that pregnant women should intentionally spend time sitting in heavy traffic or sniffing fungi for the sake of their babies. Instead, the findings help explain how exposure to substances in the womb might affect offspring down the line -- an area of research that's still defined by unknowns.

"So much has to do with the dose and timing in ways we don't understand," said Rachel Miller, an allergist, pulmonologist and immunologist at Columbia University in New York. "It does not mean that prenatal exposure to mold in pregnant women could reduce the risk of asthma in kids. It does not mean that at all."

"It suggests that prenatal exposure can be relevant in risks for asthma," she added. "It's complex."

The link between exposure and allergies goes both ways. Many studies have shown that small children are more likely to develop asthma and allergies if they're exposed to certain substances both in the womb and after birth. Aggravators include tobacco smoke, air pollution, cockroach allergens, dust mites and diesel exhaust.

Some types of exposure, on the other hand, seem to be protective. Kids who live on farms or have dogs, for example, have lower rates of hay fever, asthma and other allergic diseases.

Miller and colleagues wanted to see how prenatal exposure to certain allergens might affect mice after they've become adults. The researchers chose to focus on mold and diesel exhaust because evidence suggests that both contribute to high rates of asthma in inner cities.

For their experiment, the scientists exposed pregnant mice to mold allergens, diesel exhaust, both, or neither. Then they exposed the same substances to offspring at nine or 10 weeks old, which is early adulthood in mice.

Results, published in the journal Allergy, Asthma & Clinical Immunology, showed that, compared to offspring of mothers who inhaled a saline solution while pregnant, offspring of mothers who had been exposed to mold had lower rates of antibodies associated with allergies and less asthma-like airway inflammation. When the mothers also inhaled diesel exhaust, their adult offspring fared even better.

While the findings agree with some other studies and disagree with others, each step forward should help elucidate a murky and complicated field, said James Gern, a pediatric allergist and immunologist at the University of Wisconsin, Madison.

"I think there are more questions than answers right now," he said. "It's possible that prenatal exposures do affect immune or lung development. I think it's a real open question which way those associations will go."

While it may be tempting to extrapolate the findings to humans, it's too early to seek advice in the new results, especially because mice don't actually develop true asthma.

"These experimental models that are exposing pregnant mice to various things and looking at the effects on their pups can be instructive," Gern said. "But it's important to know that there may be big differences in human diseases."