Results of a new US study published today have looked at whether cleaning products are linked to an increased risk of breast cancer. They appear to show that women who say they used such products in the past are more likely to have breast cancer.

But Cancer Research UK said that the results do not prove a link between cleaning products and breast cancer, and that the findings may have been distorted as a result of patients' existing beliefs about the health risks of chemicals.

Writing on the charity's blog, Jessica Harris, Cancer Research UK's health information officer, pointed out that no link was observed between women who didn't already believe that chemicals increased cancer risk.

"Cleaning products were only linked to breast cancer risk in women who thought that chemicals and pollution cause breast cancer. In those who didn't hold to such beliefs, the link disappeared," she wrote.

The research was carried out by scientists at the Silent Spring Institute in the US and is published in the journal Environmental Health.

Scientists carried out telephone interviews with 787 breast cancer patients and a further 721 women who were cancer-free to find out about their use of cleaning products.

Women were also questioned on their beliefs about the causes of breast cancer, and about established and possible risk factors.

The researchers found that women who claimed to use more air fresheners and products for mould and mildew control tended to be more likely to have breast cancer than those who rarely used these products.

Study author Dr Julia Brody said that women who reported the highest combined cleaning product use were twice as likely to have had breast cancer compared to those with the lowest reported use.

"Use of air fresheners and products for mould and mildew control were associated with increased risk. To our knowledge, this is the first published report on cleaning product use and risk of breast cancer," she said.

However, Dr Brody noted that recall bias may have contributed to the findings, as women with breast cancer who believed chemicals and pollutants greatly increased an individual's risk of the disease were found to be more likely to report high product usage.

She observed: "When women are diagnosed with breast cancer, they often think about what happened in the past that might have contributed to the disease. As a result, it may be that women with breast cancer more accurately recall their past product use or even over-estimate it.

"Or it could also be that experience with breast cancer influences beliefs about its causes. For example, women diagnosed with breast cancer are less likely to believe heredity contributes 'a lot', because most are the first in their family to get the disease."

The researchers said that their results may have been influenced by recall bias and that this makes it impossible to draw conclusions from their study.

They recommended prospective studies of cleaning product use and breast cancer incidence to clarify whether or not there is a link between the two.

Cancer Research UK agreed. "There need to be larger studies where people report their use of cleaning products upfront, and are then followed up over time, to get a more accurate picture of the effect of these products," wrote Harris.

"Prospective studies like this aren't as prone to recall bias, and would be much more reliable. But until those studies are done, we won't know whether or not there's any link. For the moment, there's certainly little good reason for concern."