| All users | Semi-permanent dye users | Permanent dye users | Dark permanent‡ dye users | |||||
| Cases/controls | OR (95% CI) | Cases/controls | OR (95% CI) | Cases/controls | OR (95% CI) | Cases/controls | OR (95% CI) | |
| Total | 175/679 | 90/313 | 135/524 | 101/343 | ||||
| Hair colouring product use | ||||||||
| Never | 59/179 | 1.0 | – | – | – | |||
| Ever | 116/500 | 0.8 (0.5 to 1.1) | 31/134 | 0.7 (0.4 to 1.2) | 76/345 | 0.8 (0.5 to 1.1) | 42/164 | 0.8 (0.5 to 1.3) |
| Dye colour used most frequently | ||||||||
| Light blonde | 30/150 | 0.8 (0.5 to 1.3) | 3/12 | 0.8 (0.2 to 3.0) | 27/133 | 0.8 (0.5 to 1.4) | – | |
| Dark blonde | 11/62 | 0.6 (0.3 to 1.3) | 3/14 | 0.7 (0.2 to 2.5) | 7/48 | 0.5 (0.2 to 1.2) | – | |
| Red | 6/50 | 0.4 (0.2 to 1.0) | 2/10 | 0.8 (0.2 to 3.7) | 4/39 | 0.4 (0.1 to 1.0) | 4/39 | 0.3 (0.1 to 1.0) |
| Light brown | 19/49 | 1.3 (0.7 to 2.5) | 8/19 | 1.5 (0.6 to 3.6) | 9/28 | 1.1 (0.5 to 2.5) | 9/28 | 1.1 (0.5 to 2.5) |
| Medium brown | 24/85 | 0.9 (0.5 to 1.6) | 4/36 | 0.3 (0.1 to 1.0) | 17/43 | 1.4 (0.7 to 2.6) | 17/43 | 1.4 (0.6 to 3.7) |
| Dark brown/black | 23/104 | 0.6 (0.3 to 1.1) | 11/43 | 0.7 (0.3 to 1.6) | 12/54 | 0.6 (0.3 to 1.2) | 12/54 | 0.6 (0.3 to 1.3) |
| Age at first use | ||||||||
| ⩾48 years | 29/131 | 0.6 (0.4 to 1.0) | 13/46 | 0.7 (0.3 to 1.3) | 13/75 | 0.5 (0.2 to 0.9) | 8/40 | 0.5 (0.2 to 1.2) |
| 38–<48 years | 31/124 | 0.8 (0.5 to 1.4) | 8/36 | 0.8 (0.3 to 1.8) | 23/82 | 0.9 (0.5 to 1.7) | 17/50 | 1.2 (0.6 to 2.2) |
| 30–<38 years | 27/100 | 1.0 (0.6 to 1.8) | 5/22 | 1.0 (0.3 to 2.7) | 19/76 | 0.9 (0.5 to 1.7) | 10/34 | 1.0 (0.5 to 2.3) |
| <30 years | 27/145 | 0.7 (0.4 to 1.3) | 5/30 | 0.6 (0.2 to 1.8) | 21/112 | 0.7 (0.4 to 1.4) | 7/40 | 0.5 (0.2 to 1.2) |
| Year first used | ||||||||
| ⩾1980 | 38/210 | 0.7 (0.4 to 1.1) | 16/64 | 0.7 (0.4 to 1.4) | 55/209 | 0.6 (0.5 to 1.3) | 30/97 | 0.7 (0.3 to 1.4) |
| <1980 | 76/290 | 0.8 (0.6 to 1.2) | 15/70 | 0.8 (0.4 to 1.5) | 21/136 | 0.8 (0.3 to 1.1) | 12/67 | 0.9 (0.5 to 1.5) |
| Duration of use | ||||||||
| <7 years | 26/134 | 0.7 (0.4 to 1.2) | 12/59 | 0.6 (0.3 to 1.3) | 12/70 | 0.7 (0.3 to 1.4) | 6/30 | 0.7 (0.3 to 1.7) |
| 7–<15 years | 28/122 | 0.8 (0.5 to 1.4) | 9/31 | 1.0 (0.4 to 2.2) | 18/85 | 0.8 (0.4 to 1.6) | 10/48 | 0.8 (0.4 to 1.6) |
| 15–<28 years | 27/131 | 0.6 (0.4 to 1.1) | 6/25 | 0.8 (0.3 to 2.0) | 17/98 | 0.6 (0.3 to 1.0) | 12/50 | 0.8 (0.4 to 1.5) |
| ⩾28 years | 30/112 | 0.8 (0.5 to 1.3) | 2/19 | 0.3 (0.1 to 1.4) | 28/91 | 0.9 (0.5 to 1.6) | 14/35 | 1.1 (0.5 to 2.2) |
| Number of lifetime applications | ||||||||
| <52 | 22/146 | 0.5 (0.3 to 0.9) | 10/57 | 0.6 (0.3 to 1.2) | 10/82 | 0.5 (0.2 to 1.0) | 4/38 | 0.4 (0.1 to 1.1) |
| 52–<130 | 23/82 | 1.0 (0.6 to 1.7) | 6/19 | 1.1 (0.4 to 2.9) | 16/61 | 0.9 (0.5 to 1.8) | 10/36 | 0.9 (0.4 to 2.0) |
| 130–<240 | 22/88 | 0.8 (0.4 to 1.4) | 1/21 | – | 20/65 | 1.0 (0.5 to 1.8) | 16/34 | 1.5 (0.8 to 3.0) |
| ⩾240 | 24/79 | 0.9 (0.5 to 1.6) | 6/11 | 1.5 (0.5 to 4.4) | 17/62 | 0.8 (0.4 to 1.6) | 9/27 | 1.0 (0.4 to 2.3) |
*ORs adjusted for age and race; never users used as referent group for all comparisons; †sums may not add up to total due to missing responses for some questions; ‡dark permanent dye users include the use of red, light brown, medium brown and dark brown/black colours. OR, odds ratio.