Table 3.

Risk of breast cancer in relation to duration of hair relaxer use among users with frequency ≥7 times per year according to age (<45, ≥45 y) in the Black Women's Health Study

Duration of hair relaxer use (y)
Nonuse*1-45-910-1415-19≥20
Age <45 y
    Cases1212101822
    Person-years8,8759604,14113,88317,65715,776
    IRRReference0.850.580.911.070.84
    95% CI0.11-6.520.13-2.620.38-2.160.51-2.250.42-1.71
Age ≥45 y
    Cases414491257
    Person-years11,13498214182374337816,694
    IRRReference1.160.821.151.131.03
    95% CI0.41-3.260.29-2.310.56-2.390.58-2.170.68-1.56
  • * Never used or <1 y of use.