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To evaluate the association between personal hair dye use and risk of multiple myeloma among women.
We conducted a population-based case-control study to identify 175 cases of multiple myeloma and 679 controls. Cases and controls were interviewed in-person by trained interviewers regarding their use of hair coloring products. Subjects were asked to report the type and color of the hair coloring product used, age at first use, age use stopped, duration, and the frequency of use per year. Odds ratios (ORs) and 95% confidence intervals (CI) were estimated using unconditional logistic regression to compare never users with four exposure groups: all users, ever semi-permanent users, ever permanent users, and dark permanent users (most frequent use).
Results: We did not find any association between ever reporting hair coloring product use and myeloma risk among all users: OR=0.8, 95% CI=0.5–1.1, semipermanent users: OR=0.7, 95% CI=0.4–1.2, permanent users: OR=0.8, 95% CI=0.5–1.1, or dark permanent users: OR=0.8, 95% CI=0.5–1.3. There were no significant associations among women who used hair dyes before 30 years of age, who started use before 1980, who had ≥240 lifetime applications, or for dark permanent users with 28 or more years of use.
We did not find any evidence of an association between hair coloring product use and myeloma risk. However, given the conflicting body of literature on hair coloring product use and risk of multiple myeloma, this question should be further evaluated in larger studies or consortia, and in high risk groups.
Multiple myeloma is a form of cancer in which malignant plasma cells accumulate in the bone marrow and whose etiology is not well understood (1). Etiologic factors for multiple myeloma are not well established. Elevated risks have been linked with increasing age, male gender, African heritage and several other postulated exposures like pesticides, radiation, medication use, lower education, income/socioeconomic status and other occupational exposures (2). Early reports of an excess risk of myeloma among women working as cosmetologists or hairdressers (3,4) led to further investigations of an association between personal use of hair coloring products and myeloma risk (5–9). Hair dye ingredients, which vary by color and product type, have been shown to have carcinogenic properties (10). Although the chemical constituents of hair dyes have changed since the 1980s, including the removal of some known carcinogens, some recent products may still contain carcinogens (11). The impact of these changes, however, has not sufficiently been evaluated in epidemiologic studies. Thus, we conducted a population-based case-control study among U.S. women in the state of Connecticut to evaluate the association between personal hair dye use and risk of multiple myeloma.
A detailed description of the study population has been given elsewhere (12). Briefly, cases consisted of female residents of Connecticut aged 21–84, diagnosed with multiple myeloma between January 1, 1996 and December 31, 2002 and identified through the Connecticut Tumor Registry. A total of 186 cases completed in-person interviews which corresponded to a response rate of 57%. Population-based controls were the same controls selected for a parallel study of non-Hodgkin lymphoma (NHL) (13) and were identified using random digit dialing (RDD) and the Centers for Medicare and Medicaid Services (CMS). Controls were frequency matched to the NHL cases by age within 5-year age groups. A total of 717 controls completed in-person interviews; the response rate was 69% for RDD controls and 47% for CMS controls. After exclusions for missing data, our analyses were based on 175 cases and 679 controls.
Cases and controls were interviewed in-person by trained interviewers. Study subjects were provided a list of hair coloring processes and products, and were asked whether they used any of the items on the list at any time in their lives. Pictures of hair product labels were shown to study participants to facilitate their recall. If the subjects reported any of these products, they were then asked to report the time period in which they had used the corresponding hair coloring product. For each time period, subjects were asked to report the type and color of the hair coloring product used, age at first use, age use stopped, duration, and the frequency of use per year. Separate time periods were determined for each change in either product or color.
Odds ratios (ORs) and 95% confidence intervals (CI) were estimated using unconditional logistic regression with adjustments for age (<50, 50–59, 60–69, 70+), and race (White, Black). Other variables including drinking, smoking, education, BMI, and SES were evaluated as potential confounders but were ultimately excluded from models because they did not change OR estimates by more than ten percent. ORs and 95% CIs were obtained for ever use of hair coloring products (never/ever) and for dye color used most frequently (light blonde, dark blonde, red, light brown, medium brown, dark brown/black). Factors such as age at first use, year of first use, duration and number of applications were also considered. Age, duration, and frequency categories are based on quartiles of the distribution among the cases due to small numbers. Analyses compared never users to four exposure groups: all users, ever semi-permanent users, ever permanent users, and dark permanent users (most frequent use). Separation of these usage groups is indicated due to several findings that implicate dark permanent use as more deleterious (5,9,14). All statistical analyses were conducted using SAS software, version 8 (SAS Institute, Inc., Cary, North Carolina).
The demographic characteristics of the study subjects were explored; a higher proportion of controls (21%) than cases (7%) were under 50 years of age because the controls had been frequency-matched to the NHL case series, however all analyses were age-adjusted. The majority of subjects were white, with a higher proportion of cases (13%) than controls (4%) being black. Cases tended to have less formal education, greater BMI, and smoke and drink alcohol less than the controls.
We did not find any association between ever reporting hair coloring product use and myeloma risk, OR=0.8, 95% CI=0.5–1.1 (Table 1). Risks by hair dye color ranged from 0. 0.4, 95% CI=0.2–1.0 for users of red colors to 1.3, 95% CI=0.7–2.5 for users of light brown color however there were no consistent patterns among all users, semi-permanent users, permanent users, or women who used dark permanent dyes most frequently. There were no significant associations among women who used hair dyes before 30 years of age, who started use before 1980, or with ≥240 lifetime applications. Similarly, no association was observed for dark permanent users with 28 or more years of use, OR=1.1, 95% CI=0.5, 2.2, or among any other user type.
Hair coloring products are known to contain several chemical compounds including aromatic amines which have been found to be mutagenic and carcinogenic in several experimental studies (10). The parallel analysis of NHL found an increased risk among women who used hair dyes before 1980 and for those who use dark permanent dyes for 25 years or more (13). This population-based case-control study showed no association between use of hair coloring products and risk of multiple myeloma. Our study is consistent with null associations reported in three case-control studies (7,8,15) and two cohort studies (6,16). Two case-control studies and one cohort study, however, have reported hair color use as a risk factor for myeloma especially among those reporting use of dark hair dyes for long periods of time (5,9,14); we did not observe this association here. Only one case-control study evaluated the product type (9), only two studies examined the frequency of use (5,9), and several of these previous reports are based on smaller numbers than those presented here.
Several strengths and potential limitations of the study design should be considered in interpreting our null findings. In this study, we collected lifetime histories of hair coloring product use with detailed questions on type, shade, duration of use, age at first use, and number of applications. This allowed us to calculate risk for various levels and categories of exposure, including time period of use. As with previous studies, our ability to evaluate hair dye use and myeloma risk was limited by a small sample size (# exposed: cases = 116; controls = 500) that prevented us from fully evaluating hair dye use and any subsequent risk overall and within well-known high risk groups, such as blacks and dark permanent dye users. The differing participation rates between cases and controls and potential selection bias due to low response rates is also a concern. Although no information was available on the characteristics of non-participants, we used vital statistics data to compare the demographic profile of participating controls with that of the Connecticut population from which they were drawn. In terms of demographic characteristics controls were similar to the general population (17). Therefore, it seems unlikely that controls were misrepresented in our study regarding exposure-related characteristics.
In summary, we did not find any evidence of an association between hair coloring product use and myeloma risk. However, given the conflicting body of literature on hair coloring product use and risk of multiple myeloma, this question should be further evaluated in larger studies or consortia, using well characterized hair dye information and particularly among high risk groups.
This research was supported by the Intramural Research Program of the National Institutes of Health (National Cancer Institute, Division of Cancer Epidemiology and Genetics). Certain data used in the study were obtained from the Connecticut Tumor Registry, Connecticut Department of Public Health. The authors thank the institutions that allowed access to diagnostic materials and pathology reports, including the following hospitals: Charlotte Hungerford Hospital, Danbury Hospital, Greenwich Hospital, Griffin Hospital, Hartford Hospital, Johnson Memorial Hospital, Middlesex Hospital, Lawrence and Memorial Hospital, New Britain General Hospital, Bradley Memorial Hospital, Norwalk Hospital, St. Francis Hospital and Medical Center, St. Mary’s Hospital, Hospital of St. Raphael, St. Vincent’s Medical Center, Stamford Hospital, William W. Backus Hospital, Waterbury Hospital, Yale-New Haven Hospital, Manchester Memorial Hospital, Rockville General Hospital, Bridgeport Hospital, Windham Hospital, Sharon Hospital, Milford Hospital, New Milford Hospital, Bristol Hospital, MidState Medical Center, and Day-Kimball Hospital.