Exposure to cleaning products while in the womb could be linked to persistent wheezing in young children, University of Bristol research suggests.
Women were asked about their use of cleaning products
Experts looked at families' use of a range of products such as bleach, paint stripper and carpet cleaners.
Children born into the 10% of families which used these products the most were twice as likely to suffer from wheezing as those who used the least.
The study of 14,000 children from birth is published in the journal Thorax.
The researchers said, while their study suggested a link between prenatal exposure and wheezing, exposure after birth could also be a factor.
Further research is under way to look for physiological changes in the children's lungs which would indicate the effect had occurred while they were in the womb.
Wheezing can be a sign a child will go on to develop asthma.
The study, which is part of the University of Bristol's Children of the 90s research, involved 7,019 families.
Pregnant women were asked how often they used common household cleaning products.
The 11 most common were disinfectant (used by 87.4%), bleach (84.8%),
carpet cleaner (35.8%), window cleaner (60.5%), dry cleaning fluid (5.4%),
aerosols (71.7%), turpentine/white spirit (22.6%), air fresheners - spray,
stick or aerosol (68%), paint stripper (5.5%) , paint or varnish (32.9%)
and pesticides/insecticides (21.2%).
The researchers then calculated the total chemical burden for each family, depending on how often they used each product - then they compared it with each mother's report on whether her child had experienced wheezing.
The children were followed until they were three-and-a-half years old.
It was found 6.2% (432 children) had a persistent wheeze from being a baby.
Just over 70% of the children had never experienced wheezing, 19% wheezed as babies but not when they were older, and 3.5% developed wheezing problems after the age of two-and-a-half.
The more frequently the chemicals were used, the higher the risk that the young
child would have persistent wheezing.
The link remained even after other factors, such as parental smoking, damp housing, and family history of asthma were taken into account.
Other studies have shown people working as cleaners are at increased risk of developing asthma, and that toddlers exposed to fumes from solvents and cleaning products at home are also at high risk.
Dr Andrea Sherriff, who led the study, said: "We can't say the products caused the wheezing. We can only say we observed an association."
Indoor air quality
Dr Sherriff said: "Pregnant women should be reassured that this is simply an observational study. It does not offer conclusive proof that this is causing a rise in asthma.
"But also, it would be sensible to use these things in moderation."
She added: "Further research will identify whether this effect persists into later childhood and will attempt to identify the specific components responsible."
Dr Matt Hallsworth, of the charity Asthma UK, said: "There is gathering evidence that environmental exposures early in life, including in the womb, may influence the development of asthma.
"This large study provides some evidence that increasing exposure to household chemicals during pregnancy may be linked to an increased risk of a child wheezing in the first few years of life."
He added: "There has been much debate about whether outdoor air pollution increases the risk of developing asthma.
"This study reminds us that we should also consider the quality of the indoor air we breathe and how it may affect the health of our children's lungs."
But a spokesman for the UK Cleaning Products Industry Association said: "Based on the information currently available in the new study, and given the number of other factors that need to be taken into consideration, the correlations reported cannot be said to show household chemicals to be a cause of wheezing, let alone a 'rise in asthma'.
"On the contrary, household and institutional cleaning products, antimicrobial products, and pest management products, play a critical role in protecting public health, including against allergies."