Table 2:
Hair dye and straightener exposure in the 12 months prior to enrollment and incident breast cancer, Sister Study, 2003–2009.
| Person-years | Events | Age-adjusted HR (95% CI) | Adjusted HR* (95% CI) | |
|---|---|---|---|---|
| 2,794 | ||||
| Permanent hair dye | ||||
| Personal use in the 12 months before enrollment | ||||
| No use† | 173,213 | 1,235 | Ref | Ref |
| Any use | 213,125 | 1,559 | 1.07 (1.00, 1.16) | 1.09 (1.01 1.17) |
| <4 times per year | 89,931 | 634 | 1.07 (0.97, 1.17) | 1.08 (0.98, 1.19) |
| Every 5–8 weeks, 1+ per month | 123,194 | 925 | 1.08 (0.99, 1.18) | 1.09 (1.00, 1.19) |
| p for trend | 0.05 | |||
| Dye color | ||||
| None | 173,213 | 1,235 | Ref | Ref |
| Light colors only | 92,847 | 713 | 1.10 (1.00, 1.21) | 1.12 (1.02, 1.23) |
| Dark colors only | 94,908 | 683 | 1.07 (0.97, 1.18) | 1.08 (0.98, 1.19) |
| Light and dark colors | 23,009 | 144 | 0.95 (0.80, 1.14) | 0.96 (0.81, 1.14) |
| Years of personal use | ||||
| None | 135,033 | 965 | Ref | Ref |
| < 5 | 63,995 | 458 | 1.07 (0.96, 1.20) | 1.07 (0.96, 1.20) |
| 5 or more | 182,209 | 1,340 | 1.04 (0.96, 1.13) | 1.05 (0.96, 1.14) |
| Applied to others | ||||
| No use† | 357,754 | 2,606 | Ref | Ref |
| Any use | 28,585 | 188 | 0.97 (0.84, 1.13) | 0.99 (0.85, 1.15) |
| <4 times per year | 24,012 | 160 | 0.99 (0.85, 1.17) | 1.01 (0.86, 1.19) |
| Every 5–8 weeks, 1+ per month | 4,573 | 28 | 0.86 (0.59, 1.25) | 0.88 (0.61, 1.28) |
| p for trend | 0.7 | |||
| Semi-permanent dye | ||||
| Personal use in the 12 months before enrollment | ||||
| No use† | 315,173 | 2,311 | Ref | Ref |
| Any use | 71,165 | 483 | 0.96 (0.87, 1.05) | 0.96 (0.87, 1.06) |
| <4 times per year | 43,032 | 295 | 0.99 (0.88, 1.12) | 0.99 (0.88, 1.12) |
| Every 5–8 weeks, 1+ per month | 28,133 | 188 | 0.91 (0.78, 1.05) | 0.91 (0.78, 1.06) |
| p for trend | 0.3 | |||
| Dye color | ||||
| None | 315,173 | 2,311 | Ref | Ref |
| Light colors only | 20,860 | 145 | 0.94 (0.79, 1.11) | 0.95 (0.80, 1.13) |
| Dark colors only | 42,236 | 282 | 0.95 (0.84, 1.08) | 0.96 (0.84, 1.09) |
| Light and dark colors | 3,869 | 21 | 0.79 (0.51, 1.21) | 0.79 (0.51, 1.21) |
| Years of personal use | ||||
| None | 270,992 | 2,026 | Ref | Ref |
| < 5 | 54,574 | 355 | 0.90 (0.80,1.01) | 0.90 (0.80,1.01) |
| 5 or more | 52,540 | 356 | 0.89 (0.80,1.00) | 0.90 (0.80,1.00) |
| Applied to others | ||||
| No use† | 373,614 | 2,689 | Ref | Ref |
| Any use | 12,724 | 105 | 1.24 (1.02, 1.51) | 1.28 (1.05,1.56) |
| <4 times per year | 10,794 | 88 | 1.24 (1.00, 1.53) | 1.27 (1.03,1.58) |
| Every 5–8 weeks, 1+ per month | 1,930 | 17 | 1.26 (0.78, 2.04) | 1.31 (0.81, 2.12) |
| p for trend | 0.02 | |||
| Temporary dyes (rinses) | ||||
| Personal use in the 12 months before enrollment | ||||
| No use | 356,833 | 2,573 | Ref | Ref |
| Any use | 29,506 | 221 | 1.04 (0.90,1.19) | 1.05 (0.91,1.21) |
| Chemical straighteners | ||||
| Personal use in the 12 months before enrollment | ||||
| No use† | 351,502 | 2,543 | Ref | Ref |
| Any use | 34,837 | 251 | 1.09 (0.95,1.24) | 1.18 (0.99,1.41) |
| <4 times per year | 16,279 | 107 | 0.98 (0.81, 1.19) | 1.07 (0.86, 1.34) |
| Every 5–8 weeks, 1+ per month | 18,558 | 144 | 1.18 (0.99, 1.39) | 1.31 (1.05, 1.63) |
| p for trend | 0.02 | |||
| Applied to others | ||||
| No use† | 376,147 | 2,716 | Ref | Ref |
| Any use | 10,192 | 78 | 1.20 (0.96,1.51) | 1.27 (0.99,1.62) |
| <4 times per year | 7,619 | 62 | 1.28 (0.99,1.65) | 1.35 (1.03,1.77) |
| Every 5–8 weeks, 1+ per month | 2,573 | 16 | 0.97 (0.59, 1.59) | 1.03 (0.62,1.70) |
| p for trend | 0.2 |
*
models adjusted for age, race, education, ever oral contraceptive use (OC), parity, age at first birth, smoking status, BMI, age at menarche, menopausal status.
†
For hazard ratio estimates associated with personal use in the 12 months before enrollment and application to others in the 12 months before enrollment, “No use” is the referent category for “Any use”. For frequency of use, “No use” is also the referent category for “<4 times per year” and “Every 5 weeks, 1+month” and the p for trend is provided.