Hair chemicals may increase breast cancer risk: A meta-analysis of 210319 subjects from 14 studies.

<h4>Background</h4>The association between personal hair dye use and breast cancer risk is currently debated. The aim of this work is to investigate the association between the use of hair care products and breast cancer risk in women.<h4>Methods</h4>Based on the PRISMA-IPD statement, the PubMed, Embase, Cochrane Library, Web of Science, OVID and Scopus databases were used to identify eligible studies published from inception to 22 April 2020. A pooled odds ratio (OR) with a 95% confidential interval (CI) was calculated to assess this correlation via fixed- or random-effect Mantel-Haenszel models using a heterogeneity Chi2 test with a significance level of p<0.1. All statistical tests were performed using StataSE software (version 12.0).<h4>Results</h4>The analyzed data comprised 14 eligible studies with 210319 unique subjects. The pooled results suggested that there was a significant association between the use of hair dyes and breast cancer occurrence (pooled OR = 1.07; 95% CI, 1.01-1.13). Regarding the individual analysis regarding the different types of hair chemicals, permanent hair dye users (pooled OR = 1.08; 95% CI, 1.03-1.14) and rinse users (pooled OR = 1.17; 95% CI, 1.02-1.35) were both found to have a significantly elevated breast cancer risk compared to natural hair subjects, whereas there was an insignificant relationship between the use of semipermanent hair dyes (pooled OR = 1.09; 95% CI, 0.92-1.28) and straighteners (pooled OR = 1.04; 95% CI, 0.96-1.14) and breast cancer risk. No impact on the overall correlation between hair dyes and breast cancer risk due to race (White vs non-White) (pooled OR = 1.05; 95% CI, 0.86-1.29), timing of use (<10 years vs ≥10 years) (pooled OR = 0.96; 95% CI, 0.85-1.08) or dye color (Darker than natural hair vs Lighter than natural hair) (pooled OR = 0.91; 95% CI, 0.62-1.32) was found.<h4>Conclusions</h4>Chemicals in hair dyes may play a role in breast carcinogenesis and increase breast cancer risk.

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