Table 1 Risk of multiple myeloma associated with hair colouring products by use characteristics* †
All usersSemi-permanent dye usersPermanent dye usersDark permanent‡ dye users
Cases/controlsOR (95% CI)Cases/controlsOR (95% CI)Cases/controlsOR (95% CI)Cases/controlsOR (95% CI)
Total175/67990/313135/524101/343
Hair colouring product use
    Never59/1791.0
    Ever116/5000.8 (0.5 to 1.1)31/1340.7 (0.4 to 1.2)76/3450.8 (0.5 to 1.1)42/1640.8 (0.5 to 1.3)
Dye colour used most frequently
    Light blonde30/1500.8 (0.5 to 1.3)3/120.8 (0.2 to 3.0)27/1330.8 (0.5 to 1.4)
    Dark blonde11/620.6 (0.3 to 1.3)3/140.7 (0.2 to 2.5)7/480.5 (0.2 to 1.2)
    Red6/500.4 (0.2 to 1.0)2/100.8 (0.2 to 3.7)4/390.4 (0.1 to 1.0)4/390.3 (0.1 to 1.0)
    Light brown19/491.3 (0.7 to 2.5)8/191.5 (0.6 to 3.6)9/281.1 (0.5 to 2.5)9/281.1 (0.5 to 2.5)
    Medium brown24/850.9 (0.5 to 1.6)4/360.3 (0.1 to 1.0)17/431.4 (0.7 to 2.6)17/431.4 (0.6 to 3.7)
    Dark brown/black23/1040.6 (0.3 to 1.1)11/430.7 (0.3 to 1.6)12/540.6 (0.3 to 1.2)12/540.6 (0.3 to 1.3)
Age at first use
    ⩾48 years29/1310.6 (0.4 to 1.0)13/460.7 (0.3 to 1.3)13/750.5 (0.2 to 0.9)8/400.5 (0.2 to 1.2)
    38–<48 years31/1240.8 (0.5 to 1.4)8/360.8 (0.3 to 1.8)23/820.9 (0.5 to 1.7)17/501.2 (0.6 to 2.2)
    30–<38 years27/1001.0 (0.6 to 1.8)5/221.0 (0.3 to 2.7)19/760.9 (0.5 to 1.7)10/341.0 (0.5 to 2.3)
    <30 years27/1450.7 (0.4 to 1.3)5/300.6 (0.2 to 1.8)21/1120.7 (0.4 to 1.4)7/400.5 (0.2 to 1.2)
Year first used
    ⩾198038/2100.7 (0.4 to 1.1)16/640.7 (0.4 to 1.4)55/2090.6 (0.5 to 1.3)30/970.7 (0.3 to 1.4)
    <198076/2900.8 (0.6 to 1.2)15/700.8 (0.4 to 1.5)21/1360.8 (0.3 to 1.1)12/670.9 (0.5 to 1.5)
Duration of use
    <7 years26/1340.7 (0.4 to 1.2)12/590.6 (0.3 to 1.3)12/700.7 (0.3 to 1.4)6/300.7 (0.3 to 1.7)
    7–<15 years28/1220.8 (0.5 to 1.4)9/311.0 (0.4 to 2.2)18/850.8 (0.4 to 1.6)10/480.8 (0.4 to 1.6)
    15–<28 years27/1310.6 (0.4 to 1.1)6/250.8 (0.3 to 2.0)17/980.6 (0.3 to 1.0)12/500.8 (0.4 to 1.5)
    ⩾28 years30/1120.8 (0.5 to 1.3)2/190.3 (0.1 to 1.4)28/910.9 (0.5 to 1.6)14/351.1 (0.5 to 2.2)
Number of lifetime applications
    <5222/1460.5 (0.3 to 0.9)10/570.6 (0.3 to 1.2)10/820.5 (0.2 to 1.0)4/380.4 (0.1 to 1.1)
    52–<13023/821.0 (0.6 to 1.7)6/191.1 (0.4 to 2.9)16/610.9 (0.5 to 1.8)10/360.9 (0.4 to 2.0)
    130–<24022/880.8 (0.4 to 1.4)1/2120/651.0 (0.5 to 1.8)16/341.5 (0.8 to 3.0)
    ⩾24024/790.9 (0.5 to 1.6)6/111.5 (0.5 to 4.4)17/620.8 (0.4 to 1.6)9/271.0 (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.