Scientists believe if a mother-to-be is stressed it can influence the development of her baby's immune system.
A team of US researchers analysed levels of immunoglobulin E (IgE) - a protein linked to allergies - in the umbilical cord blood of 387 infants. They found higher levels of IgE among babies whose mothers had experienced stress while pregnant.
Previous animal experiments had suggested that a combination of stress and allergy triggers during pregnancy can affect an offspring's immune system.
In the new study, mothers were exposed to varying levels of dust mite allergen.
Stress appeared to magnify the effect of the dust mite on foetuses. Even women with low exposure had babies with raised IgE if they had been stressed.
Study leader Dr Rosalind Wright, from Brigham & Women's Hospital and Harvard Medical School in Boston, Massachusetts, said: "Certain substances in the environment that cause allergies, such as dust mites, can increase a child's chance of developing asthma and the effects may begin before birth.
"This further supports the notion that stress can be thought of as a social pollutant that, when 'breathed' into the body, may influence the body's immune response similar to the effects of physical pollutants like allergens, thus adding to their effects."
The findings were presented at the American Thoracic Society's 2008 International Conference in Toronto, Canada.
Have you filled out the latest nursinginpractice.com online survey on cardiovascular disease? Click here to complete it.
TheNursing in Practice Awards 2008 deadline is looming (23 May 2008).Entering is easy and you can nominate yourself or someone you know whoyou think is deserving. Don't miss out on this chance to win £500. Formore information go to www.nursinginpractice.com/awards