Use of hair colouring products and breast cancer risk: a case–control study in Connecticut
Introduction
Hair colouring products have been shown to contain mutagenic and carcinogenic compounds 1, 2, 3. However, epidemiological studies of hair colouring product use and cancer risk, including breast cancer, have yielded inconclusive results. A recent study by Cook and colleagues [4] from the western Washington state in the United States of America (USA) found that the use of hair colouring products was associated with a 30% borderline significantly increased risk of breast cancer. Among women who used two or more methods of hair colouring applications, ever use of any hair colouring products was associated with a 2-fold increased risk, 3-fold among those who had a total lifetime experience of more than 90 episodes, and almost 6-fold among those who had a total lifetime use of hair colouring applications for more than 2400 min. However, because of the lack of an association between exclusive use of a single type of hair colouring application and breast cancer risk, the authors considered that hair colouring application does not influence breast cancer risk among reproductive-age women.
Considering that mutagenic and carcinogens were historically found in hair dye products 5, 6, and the potential carcinogenic effect of hair dye products observed by the recent epidemiological studies 4, 7, 8, we conducted a detailed examination of the association between breast cancer risk and hair colouring product applications using data from a case–control study conducted in Connecticut in the USA.
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Study population
A description of the study population and methods has been given elsewhere in Ref. [9]. Briefly, cases for the case–control study were histologically-confirmed, incident breast cancer patients (ICD-O, 174.0–174.9) who either had breast-related surgery at the Yale-New Haven Hospital (YNHH), in New Haven County, or who were residents of Tolland County, Connecticut, between 1 January 1994 and 31 December 1997. Subjects were restricted to women 30–80 years of age who had no previous diagnosis of
Results
Cases were slightly older than controls despite frequency matching. Therefore, age was controlled in all subsequent analyses so as to reflect the study design. Women with a later age at first full-term pregnancy showed a significantly increased risk (Table 1). In comparison to those less than age 20 years at first full pregnancy, the ORs were 1.6 (95% CI 1.1–2.4) and 1.8 (95% CI 1.1–2.7) for those having first full-term pregnancy at ages 20–25 years and over age 25 years, respectively. Women
Discussion
In this case–control study, we found no overall association between hair colouring product use and breast cancer risk. While there was a suggestion of an increased risk of breast cancer among those who used semi-permanent hair dye products, none of the ORs were statistically significant, and there was no clear pattern of an increased risk with increased duration and extent of use. Therefore, chance alone may account for the observed results for semi-permanent colour use. We also did not find an
Acknowledgements
This study is supported by a grant #CA-62986 from the National Cancer Institute/National Institute of Environmental Health Science.
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