“Houseproud women with spotless bathrooms could be twice as likely to get breast cancer,” reported The Sun .

This research asked women with and without breast cancer about their prior use of household cleaning products. It found that women with breast cancer were more likely to recall using cleaning products more frequently than women without the disease.

As the newspapers report, this research is limited by a potential recall bias. All the women were asked if they believed chemicals and pollutants caused cancer. Their answers showed that only women who believed chemicals and pollutants can cause cancer demonstrated an association between cleaning product use and breast cancer. This supports the existence of bias in the breast cancer patients, suggesting that they may have remembered using cleaning products more than they actually did.

Breast cancer has numerous established and suspected risk factors. Further prospective studies are needed to see if there is an association between breast cancer and use of cleaning products.

Where did the story come from?

The study was carried out by researchers from the Silent Spring Institute in Massachusetts, US. It was funded by The Massachusetts Department of Public Health, the Susan S. Bailis Breast Cancer Research Fund and the US Centers for Disease Control and Prevention. The study was published in the peer-reviewed journal Environmental Health.

This research was generally covered well by the newspapers, which all emphasised the potential problem of recall bias in this study.

What kind of research was this?

This population-based case control study investigated whether the use of household cleaning products increases breast cancer risk.

The researchers were interested in these products because many household cleaning or pesticide products contain chemicals that affect the hormone system or are carcinogens affecting the breast tissue.

What did the research involve?

The researchers recruited 787 women from Cape Cod, Massachusetts, who had been diagnosed with breast cancer between 1988 and 1995. These women were matched to 721 women without breast cancer (controls) who were of a similar age and had lived in the same area during this period. The women were already involved in the Cape Cod Study, which assessed environmental risk factors for developing breast cancer.

All the women were asked in telephone interviews about their risk factors for breast cancer, including both established and suspected risks. This included questions on family history of breast cancer, menstrual and reproductive history, height, weight, alcohol and tobacco use, physical activity, pharmaceutical hormone use and education. The women were also asked about their cleaning product and pesticide use. All of the women were asked about their pesticide use, but use of cleaning products was questioned in only 413 of the cases and 403 of the controls.

The women were asked about what they believed could cause breast cancer. The aim of this was to determine whether women with breast cancer were more likely to recall using products they believed may have contributed to their cancer.

The breast cancer cases were also asked about their use of cleaning products and pesticides prior to the diagnosis of their disease.

Analysis was carried out for each category of cleaning and pesticide product. Overall risk from exposure to combined product categories was also calculated. For cleaning products, this was the combined frequency of use of air freshener spray, solid air freshener, oven cleaner, surface cleaner, and mould and mildew control with bleach. For pesticide use this was the combined frequency of use of insect or bug control, lawn care, outdoor and indoor plant care, insect repellent and flea control on pets. They also assessed the association between the use of each type of cleaning or pesticide individually and the risk of developing breast cancer.

What were the basic results?

Women who used cleaning products the most (the top 25%) were twice as likely to have breast cancer as those who used them the least (the bottom 25%) (odds ratio, [OR] = 2.1, 95% confidence interval [CI] 1.4 to 3.3). Solid air freshener and mould and mildew control were both associated with a 70% increased risk (both had OR = 1.7, 95% CI, 1.2 to 2.3). No association was found between breast cancer and the combined use of pesticide products or ever having used air freshener spray.

Cases and controls differed in their beliefs about the role of genetics, chemicals and pollutants in breast cancer. A smaller proportion of the cases group (42%) said that genetics contributes “a lot” to risk, compared with 66% of controls (P<0.05). More of the cases (60%) said that “chemicals and pollutants in the air or water” contribute “a lot” to breast cancer compared with 57% of the controls that thought this was the case (P<0.05).

The researchers looked at the women who said that they believed that chemicals contributed “a lot” to cancer separately to the women who did not share these beliefs. In the group of women who believed there was a chemical risk, the researchers found that the women who reported using the most cleaning products had an increased risk of breast cancer (OR 3.2, 95% CI 1.8 to 5.9). However, in women who did not believe that chemicals contributed to cancer, the highest amount of cleaning product use (top 25%) was not significantly associated with cancer risk (OR 1.2, 95% CI 0.6 to 2.6).

How did the researchers interpret the results?

The researchers say that women who reported the highest combined cleaning product use were twice as likely to have breast cancer compared with those who reported the lowest use. Use of air fresheners and products for mould and mildew control were associated with increased risk.

They recommend further prospective studies of cleaning products and breast cancer, in which participants are asked to report on their use of household cleaning products over time and are followed to assess the subsequent risks of developing breast cancer.

Conclusion

This case control study found an association between high cleaning product usage and increased risk of breast cancer. Although this was a well-designed case control study, as the researchers highlight, recall bias may have affected the results.

The researchers said that participants were asked to report their behaviour from months or years beforehand, which may have led to over- or underestimation of cleaning-product use. They also said that women with breast cancer may have recalled using these products more than they actually did, as they sought to find reasons for their breast cancer. This possibility appeared to be demonstrated in the results, as the highest use of cleaning products was only associated with increased risk of cancer among women who believed chemicals and pollutants to cause cancer.

A further limitation to this study is its size. Though the study included more than 1,400 women, cleaning product use was assessed in only 413 cases with breast cancer and 403 controls. A study such as this that aims to identify associations between a disease and a possible cause would benefit from including a much larger sample of cases and controls.

The women in this study were also almost all of white ethnicity, from a particular geographical location in the US and all aged between 60 and 80. The results might have been different if other population groups were assessed.

This is a well-conducted study. However, as the newspapers discuss, the results are subject to recall bias that may have skewed the results to show an association between cleaning products and the disease. As there is widespread exposure to cleaning and scented products, further prospective research that avoids the potential recall bias in this study is warranted, looking at whether use of cleaning products is associated with a risk of breast cancer and whether the trends observed in this study are true risk factors.

It is difficult at this stage to advise on a particular action to take, other than to follow the manufacturers' advice carefully, and to use these products in well-ventilated areas.

Analysis by Bazian

Edited by NHS Website