Although new research has found no association between personal use of permanent hair dye and the risk of most cancers or cancer-related mortality, the study found a potential link between what they call ‘cumulative dose’ of hair dye and certain types of breast cancer.
Cumulative hair dye dose was also implicated in the potential risk of ovarian cancer, the investigators noted.
Reporting in a recent issue of The BMJ, the multi-center team of researchers reported that permanent hair dye poses the greatest potential carcinogenic concern of all hair dye types. And while assessing the carcinogenic hazard of permanent hair dyes has marked public-health implications, current evidence on the topic is far from conclusive. This gap, they said, led to the current trial, The Nurses’ Health Study.
“The Nurses’ Health Study has detailed assessments of permanent hair dye exposure and validated data on a wide spectrum of potential confounders and cancer outcomes,” the authors wrote.
In total, 117,200 women were enrolled in ongoing prospective cohort study of female nurses in the United States. The participants -- all of whom were cancer-free at baseline -- reported information on personal use of permanent hair dyes, and were followed for 36 years.
The study’s primary exposure was the status, duration, frequency, and integral use (cumulative dose calculated from duration and frequency) of permanent hair dyes. Its primary outcome measure was the association between use of such dyes and the risk of both overall cancer and specific cancers, as well as cancer-related death.
A total of 20,805 cases of solid cancers (not including major non-melanoma skin cancers) occurred during the 36-year follow-up period, as well as 1,807 hematopoietic cancers, 22,560 basal cell carcinomas, and 2,792 cutaneous squamous cell carcinomas.
The study found that women who had ever used permanent hair dye demonstrated no significant increased risk of either solid cancers (hazard ratio 0.98; 95% confidence interval 0.96-1.01) or hematopoietic cancers (HR 1.00; 95% CI: 0.91-1.10) compared with non-users of such dyes.
Similarly, women who had ever used permanent hair dye did not have an increased risk of most specific cancers, including: cutaneous squamous cell carcinoma, bladder cancer, melanoma, estrogen receptor positive breast cancer, progesterone receptor positive breast cancer, hormone receptor positive breast cancer, brain cancer, colorectal cancer, kidney cancer, lung cancer, and most hematopoietic cancers). Similar results were found regarding the risk of cancer-related death (HR 0.96; 95% CI: 0.91-1.02).
Conversely, the risk of basal cell carcinoma was found to be slightly increased for ever users of hair dye (HR 1.05; 95% CI: 1.02 to 1.08).
When assessing the association between cumulative hair dye dose and cancer risk, the researchers noted that the results were inconsistent across endpoints. Indeed, dose-dependent analyses found no dose dependency for basal cell carcinoma. On the other hand, a larger cumulative dose was associated with greater/potentially greater risks of overall breast cancer. This, the researchers said, might indicate higher risks of estrogen receptor negative breast cancer, and progesterone receptor negative breast cancer, hormone receptor negative breast cancer.
“The dose-response analyses also suggested dose dependent positive associations for ovarian cancer, and a lower risk of chronic lymphocytic leukemia or small lymphocytic lymphoma,” they wrote.
When stratifying the results according to participants’ natural hair color, the study found an increased risk of Hodgkin lymphoma among women with naturally dark hair. Women with naturally light hair were found to have a greater risk of basal cell carcinoma.
The researchers concluded that while the study offers some reassurance regarding permanent hair dye use and the risk of cancer, this was not the case for all cancers, particularly basal cell carcinoma, breast cancer, and ovarian cancer.
Nevertheless, they acknowledged that the findings warrant further prospective validation in different populations, susceptibility genotypes, cancers, exposure settings, different timings, and hair dye colors. “Additionally,” they wrote, “exposure assessments should be more refined and interpreted in the light of the totality of evidence.”