Exposure to certain allergens in the womb may have a positive effect on children as they grow up, a new study has said.
The study found that when pregnant mice inhaled diesel exhaust and mould together, their offspring grew up to have fewer signs of allergies and asthma-like symptoms.
However, it doesn't mean that pregnant women should deliberately spend time sitting in heavy traffic or sniffing fungi for the sake of their babies.
"It does not mean that prenatal exposure to mould 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.
For the experiment, the scientists exposed pregnant mice to mould 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.
They found that compared to offspring of mothers who inhaled a saline solution while pregnant, offspring of mothers who had been exposed to mould 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.
"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," said James Gern, a pediatric allergist.
The findings were published in the journal Allergy, Asthma and Clinical Immunology.