Environment and Breast Cancer: Science Review

Evidence From Humans
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Does Hair Dye Use Increase the Risk of Breast Cancer? A Population-Based Case-Control Study of Finnish Women
Heikkinen, S., Pitkaniemi, J., Sarkeala, T., Malila, N., Koskenvuo, M. PLoS One. 2015. 10:8, e0135190.
Topic area
Environmental pollutant - Consumer product chemicals Hair dye
Study design
Population-based case-control
Funding agency
ZEG Berlin Center for Epidemiology and Health Rese
Study Participants
Menopausal Status
The menopausal status of women included in this study is listed here.
Analyses stratified by menopausal status
Number of Controls
Controls: 21,598
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
Cases were women aged 22-60 years living in Finland and diagnosed with in-situ or invasive breast cancer between January, 2000 and December 2007. For each case, four controls were randomly selected from the central population register and matched by birth year.
Comment about participation selection
While the number of cases and controls adds to the study's strength, the death of 1,550 breast cancer cases before the study start date suggests potential selection bias against more aggressive forms of cancer in the study population.
Exposures investigated
Self-administered questionnaire asked about number of lifetime hair dye episodes, frequency of dyeings, age at first dye use, and dye type.
How exposure was measured
Questionnaire, self-administered
Breast cancer outcome investigated
Primary incident breast cancer
Confounders considered
Other breast cancer risk factors, such as family history, age at first birth, and hormone replacement therapy use, that were taken into account in the study.
Parity, age at first birth, family history of breast cancer, age at menarche, hormonal contraceptive use, physical activity, alcohol use, BMI, and education.
Genetic characterization included
If the study analyzed relationships between environmental factors and inherited genetic variations, this field will be marked “Yes.” “No”, if not.
Strength of associations reported
Number of dye episodes:
1-2 OR 1.07 (95% CI 0.88-1.29)
3-9 OR 1.19 (95% CI 1.03-1.39)
10-34 OR 1.28 (95% CI 1.12-1.47)
35-89 OR 1.31 (95% CI 1.14-1.51)
≥ 90 OR 1.25 (95% CI 1.08-1.45)

Ever vs never:
Pre-menopausal OR 1.19 (95% CI 0.81-1.75)
Post-menopausal OR 1.25 (95% CI 1.10-1.43)

Ever vs never:
Born before 1950: OR 1.28 (95% CI 1.10-1.48)
Born 1950-1959: OR 1.20 (95% CI 1.02-1.40)
Born 1960 or after: OR 1.14 (95% CI 0.85-1.54)

Type of hair dye use, ever vs never:
Temporary dye: OR 1.32 (95% CI 1.16-1.52)
Semi-permanent dye: OR 1.31 (95% CI 1.17-1.46)
Permanent dye: OR 1.25 (95% CI 1.12-1.39)
Bleach: OR 1.25 (95% CI 1.06-1.48)
Results Comments
Significantly elevated OR for first hair dye use between ages 20-29 compared to at or after age 40. Stratification by birth cohort suggests this finding is stronger for older women (born before 1960).
Author address
Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Unioninkatu 22, FI-00130, Helsinki, Finland. Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Unioninkatu 22, FI-00130, Helsinki
Reviewers Comments
This study by using hair dye exposure beginning before the age of 20 for many participants.