Comments on: Hair dye and chemical straightener use and breast cancer risk in a large US population of black and white women.

Abstract

Dear editor, The article “Hair dye and chemical straightener use and breast cancer risk in a large US population of black and white women”1 is an extremely valuable large-scale study which has focused on the association of breast cancer (BC) with hair dyes and hair stabilizers, very frequently used industrial products containing endocrine-disrupting chemicals (EDC). Interestingly, the positive findings can be an explanation for the increasing trend of BC incidence in developing countries, because women in these areas are using industrial dyes more frequently; and for the increasing rates of BC in young age, since hair dyes which were probably used mainly on white hairs of aged people are now used very commonly in the young population. However, several points need to be addressed. First, as authors mention, only use of hair dye in the year before enrollment was questioned, and use throughout the cohort is not assessed. Therefore, hair dying in a nonuser who has got BC in year X and has colored her hair through the first X years of enrollment is overlooked. Also, how were the authors assured that nonusers did not use dyes in previous years? And, how much was the interval between use and BC? Second, results are stated to be adjusted for various variables but not for age, while age is most important when speaking about BC in a population where a great proportion are below the expected age of BC; and about hair dying, which is not likely to be distributed normally and without any relation to age of women. Third, the authors found out that application of semipermanent dye increases the risk of BC, while personal use did not. If skin absorption due to coloring of hands or inhalation of these materials causes rise in BC risk, then personal use could not be less effective. How can this result be justified? Fourth, when EDCs are to be investigated, many confounding factors should be considered. Environmental and nutritional factors are among the most important, because they can contain large proportions of these substances, produce a highly prevalent exposure, and may be very different among participants; especially between black and white women. Also, women who use hair dye more commonly generally also use more cosmetics, which contain EDCs and other probable effective ingredients. None of these has been addressed in the present study. Fifth, a weird finding that warrants re-evaluation is that postmenopausal women used hair dye less frequently than premenopausal women. Is it actually possible to accept that whitening of hair affects negatively the rate of hair coloring by women? There exist some more minor points. The authors first mention that one-third of women color their hair in the US, but in their cohort, more than half do (55%). Do they have an explanation for this difference? Also, BC is more frequent in postmenopausal women; have data about this group of participants been analyzed separately? A quick search on the internet shows how much a title about “increased risk of BC by hair dyes” can be disseminated, and how much it can alarm women. It seems reasonable to emphasize and even overemphasize two chief issues: First, as authors comment, all women in this study had a significant risk factor, which is a first-degree family history, and they were not “general population.” This point should have been quoted in the conclusion and even in the title of the manuscript. Second, the overall increase in risk was 9%, which is a slight increase. Even the 45% increase in black women remains comparable to many other minor risk factors. For example, the relative risk of BC for a woman who has had her first full-term delivery above 30 years of age is 1.93 and 2.83 if she also has a first-degree relative with BC.2 As a surgeon managing BC for many years, I have been asked many times by my eager patients if they could use hair dyes. We should not forget that these patients need to improve their quality of life, and a good appearance is one of the first steps. A recommendation to go on with white hair is disturbing to many: this point must be handled with great caution. Yours sincerely, Sadaf Alipour There is no conflict of interest to declare.