Table 4.

Associations between self-reported use of single hair products during the 10- to 13-years-of-age period and incident breast cancer by race and ethnicity in the Sister Study.

Product	Black or African American ($n=\mathrm{4,049}$)			Non-Black Hispanic/Latina ($n=\mathrm{2,104}$)			Non-Hispanic White ($n=\mathrm{39,312}$)
	Use	$n$ cases	Adjusted HR (95% CI)a	Use	$n$ cases	Adjusted HR (95% CI)a	Use	$n$ cases	Adjusted HR (95% CI)a
Shampoo	Frequentlyb	194	1.44 (0.77, 2.69)	Frequently	104	1 (Ref)	Frequently	2,756	1.07 (0.71, 1.63)
	Sometimesb	64	1.13 (0.59, 2.19)	Sometimes	11	0.63 (0.34, 1.19)	Sometimes	300	1.07 (0.70, 1.64)
	Did not useb	10	1 (Ref)	Did not use	6	0.64 (0.27, 1.49)	Did not use	23	1 (Ref)
Conditioner or rinse	Frequently	74	1.04 (0.74, 1.47)	Frequently	53	1.36 (0.84, 2.21)	Frequently	920	1.04 (0.94, 1.15)
	Sometimes	93	1.29 (0.96, 1.75)	Sometimes	33	1.27 (0.77, 2.10)	Sometimes	896	1.04 (0.95, 1.15)
	Did not use	93	1 (Ref)	Did not use	33	1 (Ref)	Did not use	1,167	1 (Ref)
Hair spray	Frequently or sometimes	49	1.11 (0.81, 1.51)	Frequently	6	0.91 (0.38, 2.15)	Frequentlyb	260	1.10 (0.97, 1.26)
				Sometimes	38	0.99 (0.66, 1.47)	Sometimesb	969	1.05 (0.97, 1.14)
	Did not use	226	1 (Ref)	Did not use	80	1 (Ref)	Did not useb	1,784	1 (Ref)
Hair styling gel or mousse	Frequently or sometimes	27	0.99 (0.66, 1.49)	Frequently or sometimes	15	0.76 (0.44, 1.31)	Frequentlyb	79	1.10 (0.87, 1.38)
							Sometimesb	371	1.00 (0.90, 1.12)
	Did not use	246	1 (Ref)	Did not use	113	1 (Ref)	Did not useb	2,605	1 (Ref)
Pomade or hair grease	Frequently	214	1.55 (0.82, 2.96)	Frequently	11	2.43 (1.27, 4.67)	Frequently	6	1.69 (0.76, 3.75)
	Sometimes	50	1.78 (0.89, 3.53)	Sometimes	11	0.79 (0.42, 1.47)	Sometimes	52	1.02 (0.77, 1.34)
	Did not use	10	1 (Ref)	Did not use	103	1 (Ref)	Did not use	3,056	1 (Ref)
Hair food	Frequently	16	1.19 (0.69, 2.04)	Frequently or sometimes	10	0.92 (0.48, 1.77)	Frequently or sometimes	9	1.18 (0.61, 2.28)
	Sometimes	46	0.93 (0.66, 1.30)
	Did not use	207	1 (Ref)	Did not use	117	1 (Ref)	Did not use	3,082	1 (Ref)

Note: Participants with missing data on the product of interest are excluded from single-product model. CI, confidence interval; HR, hazard ratio; Ref, reference.

^a Adjusted for birth cohort in $\sim 10\text{-y}$ intervals, family income level growing up (well off, middle income, low income, poor), and maximum household education level at 13 years of age (less than high school, high school graduate or equivalent, some college or technical school, 4-y degree or higher) in addition to age as the timescale.

^b Proportional hazards assumption violated for product use variable ($p<0.05$).