Do hair straighteners and relaxers really cause uterine cancer in women?

Who is correct NIEHS or people who believe NIEHS is wrong?

?As a toxicologist who have experience in risk assessment- I would like to convey my thought process to society for this case.

?“Communicating scientific research pertinently something related to toxicity and safety is not an easy job, it is quite challenging because, it mostly depends how public perceive the communication rather than exactly what is being communicated”- My opinion

?Let us understand the positives and negatives of the source study titled “Use of Straighteners and Other Hair Products and Incident Uterine Cancer” ??

?Positives- (Important and valuable information)

1.???The association of hair straighteners with uterine cancer might be plausible based on weight of evidence. In toxicological risk assessment, one always gives value for weight of evidence.

Let us see all weight of evidence available based on that this research is based:

Evidence exists prior to this study that hair products (hair dyes, skin lighteners, hair relaxers) use was associated with some risk of hormone-sensitive cancers including breast and ovarian cancer. So, a clue already exists that some chemicals in hair products may cause hormonal imbalance, that may trigger hormone-sensitive cancers.

One should note that NIEHS has no intention to do biased work. This study is part of the collection of epidemiological studies.

For readers- WoE studies:

Skin lighteners and hair relaxers – Risk factors for breast cancer (Study concluded that there is some biological plausibility and should continue to be monitored- Point to note- “Not concluded Skin lighteners and hair relaxers are direct culprits” (https://academic.oup.com/carcin/article/39/4/571/4792875)

?Hair relaxers and leave-in conditioners and oils - use may contribute to breast cancer risk (https://academic.oup.com/carcin/article/42/7/924/6278856).

Hair dyes is associated with breast cancer incidence- Study itself acknowledged the limitation about possibility of bias (https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0135190)?????

?Hair dyes, chemical relaxers and cholesterol or placenta-containing conditioners- A supportive relationship for breast cancer established (https://academic.oup.com/carcin/article/38/9/883/3866007)

?Hair dyes- risk of ovarian cancer- case-control study (https://onlinelibrary.wiley.com/doi/abs/10.1002/ijc.2910550313)

?Hair relaxer use increases uterine leiomyomata risk- (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3282879/)

Many more…..

?One need to acknowledge the science based on evidence and try to understand what the real reason would be or how much is pragmatically the risk- instead of criticizing limitations of the study- A single study cannot address all uncertainties to arrive for a concrete conclusion. It is group of studies; flock of thought processes and strong correlation will bring the real fact.

?2.???One should note, this is an epidemiological prospective cohort study- the results obtained are from humans but not from the experimental rodents- Above all studies (mentioned in point-1) are epidemiological studies and they all convey a risk not the hazard. In current world, where we typically lack 2-year carcinogenicity data on mixture of chemicals in experimental animals (I am not recommending 2-year carcinogenicity study, which is not ethical to have in consideration) which are generally used to determine carcinogenicity. It is quite fortunate we have epidemiological study, and ?one should at least acknowledge the human study and take meaningful outcome with it (In this case- whether we wish to agree with NIEHS or disagree, but the study results are valuable to use for next research- I believe this!)

Can we think ?a study with 33 947 participants aged 35-74 years who had a uterus at enrolment (2003-2009) and 10.9 years follow up study is useless, despite of above reasons?

?3.???This study has used Cox proportional hazard models, which inherently examine how specified factors influence the rate of a particular event happening (here uterine cancer) at a particular point in time. It is worthy to note this study included several co-variates such as age, race and ethnicity (African American/Black including Hispanic/Latina, Hispanic/Latina non-Black, non-Hispanic White, and all others, including Asian/Pacific Islander or American Indian), physical activity (metabolic equivalent hours per week), smoking status (never, past, or current), alcohol consumption (never or past, current , current <1 drink per day, current 1 drink per day), educational attainment (high school or less, some college, college and above), and occupational history working in beauty salons or barbershops. Reproductive history included age at menarche (younger than 13 years, 13 years and older), menopausal status (premenopausal and postmenopausal), parity (0, 1, 2, 3), oral contraceptive use (none, <2, 2 to <10, 10 years), hormone replacement therapy use (none, oestrogen alone, oestrogen plus progesterone but never oestrogen alone). Body mass index (BMI) was calculated by height and weight measured at baseline-

A statement from Personal care Products council (PCPC) (https://www.personalcarecouncil.org/statement/statement-by-kimberly-norman-ph-d-dabt-ert-personal-care-products-council-on-hair-straighteners/) that “The study does not account for a number of other differences that may be associated with increased incidence as the ‘uterine cancer cases tended to be older with an earlier age at menarche [the first menstrual period], a higher BMI, and lower physical activity” looks inappropriate because this study does considered all co-variables and it is also appreciable that the study itself has not much considered other observed associations due to limitations in their study design- So it makes sense that they considered co-variates and used the data when it has strength.

Additionally, the study suggests about sensitivity of Black women not solely on this study but based on their previous observations and prevalence- “Although, the study did not find that the relationship between straightener use and uterine cancer incidence was different by race, the adverse health effects may be greater for Black women due to higher prevalence of use” Exact excerpts from Study.

Because Black women use hair straightening or relaxer products more frequently and tend to initiate use at earlier ages than other races and ethnicities, these findings may be even more relevant for them.

The study clearly wants to address the vulnerable population (Black women) first from their sample size, despite of low black women in the current study. ?

?4.???This study would like to communicate the fact that “The association was stronger when comparing frequent use (>4 times in the past 12 months) vs never use (HR = 2.55, 95% CI = 1.46 to 4.45; Ptrend = .002)” There was a monotonic exposure-response relationship with increasing frequency of use of straighteners- By this one need to understand the frequency of use has influence on the association where we generally call Risk – Hazard × Exposure. Uterine cancer is rare cancer. One should also give importance biological plausibility rather than statistical plausibility for any rare type of cancer.

?I read the article posted by Dr. Lyle Burgoon - It is wonderful analysis. This type of evaluation is required (https://toxictruthblog.com/no-hair-relaxers-and-straighteners-arent-associated-with-uterine-cancer-risk). However, it is also worthy to note that all things cannot be addressed with statistics and math, because human biology is not simple math. Meaningful integration of math and biology will give correct outcome.

Dr. Lyle Burgoon emphasized on the facts around the base cancer rate 1.09% and the sample size where uterine cancers observed. It looks reasonable. For a time being keeping Binomial distribution aside (I am not expert statistician). For less frequent users of 14, 628 persons- 12 got uterine cancer and for more frequent users of ?15,464 persons- 26 got uterine cancer.

So, in lay man language, I agree with Dr. Lyle Burgoon if 14628 has 12 (0.82%) and 15464 has 26 (1.65%) is less than the 1.09% (332 of 30, 329). But one should also acknowledge the fact that the rate doubles (12/14628 to 26/15464) with just frequency of usage. The only point to observe is a large group with never used straighteners with high % base rate due to large sample size and less % base rate in frequent users due to less sample size should not be solely interpreted and compared as stand alone. We need to understand biology also in parallel to stats!

5.???This study itself acknowledged the fact that “Because of sample size limitations, the frequency, stratified, and sensitivity analyses are only reported for the products more frequently used, including personal use of permanent dyes, semi-permanent dyes, straighteners, and hair permanents”. Several sensitivity analyses were conducted to evaluate the robustness of study findings. First, they restricted the outcome to medically confirmed uterine cancer cases. Second, they removed physical activity from the model because physical activity may act as a confounder and/or a mediator. Costly and time consuming hairstyling practice may be a barrier to physical activity, whereas women engaging in intense physical activities may change their hairstyling practices (43,44). They excluded 1048 women who had worked in beauty salons or barbershops to eliminate the potential impact of occupational exposure. They considered simultaneous adjustment for other personal hair product use, including frequently used products and all products. Further, the first year of follow-up was excluded to assess the possibility of reverse causation. Estimates with fewer than 5 cases in any stratum in the statistical model are not reported.

?Additionally, the study excluded following women: who withdrew from the study (n = 3), who self-reported a diagnosis of uterine cancer before enrolment (n = 380), had an uncertain uterine cancer history (n = 10), had an unclear timing of diagnosis relative to enrolment (n = 59), had a hysterectomy before enrolment (n = 15 585), who did not answer any hair product use questions (n = 736), and who did not contribute any follow-up time (n = 164), resulting in 33 947 eligible women This exercise of exclusion is just to understand how coherent is the association or in other words “is the usage and outcome related”? Based on this observation. Study authors tried to avoid all confounding source of variation for the interpretation.

6.???It is also worthy to note the study itself stated “More research is warranted to replicate our findings in other settings and to identify specific chemicals driving this observed association”. So, we should avoid blaming NIEHS that “It concluded that specific straighteners and specific chemicals caused uterine cancer” No- still NIEHS has not clearly concluded the cause- They clearly stated more research is warranted.

?7.???It is also important to note the conditions around use of hair straighteners- pertinently the application at scalp level (hair skin pores and favorable percutaneous absorption) and the use of some heating process (such as flat ironing or blow drying), which will in fact create more favorable to cocktail of chemicals to enter human body. Straightener use may cause scalp lesions and burns, which facilitates the permeability of chemicals through the scalp. So based on this exercising a caution is always good for time being until the facts proven for our safety. It is also important to note neither NIEHS has suggested any regulatory to ban hair straighteners, nor regulatory took this study seriously with immediate effect and decided or policy made. So, one should understand the data and acknowledge the science and encourage some more research to really understand the fact, so that we can either agree or rule out this.

Now Let’s talk about

Negatives- (which would have taken care or improvement required in these areas to yield more meaningful outcome)

1.???As Dr. Lyle Burgoon pointed, sample size should have been little more to understand, whether it is truly positive or false positive from an angle of statistical analysis in an epidemiological study. In other words, a specific analysis in large set of people who use straighteners frequently and evaluating the confounding factors will be a point to be noted and further research to be carried out in this angle.

It is also important to note that, study was designed with an interview and self-administered questionnaires that included questions about hair product use. It is just a prospective cohort study and not a controlled experimental study. So, there is still a chance of co-exposures that could trigger uterine cancer instead of hair straighteners. Therefore, it is very important to establish real cause, because as PCPC rightly pointed the fact that “that association is not the same as causation; one does not necessarily lead to the other”

But as a public we need take cognizance about the observation that there could be a chance of association of uterine cancer with hair straighteners. So, slight reduction in usage or certain measures ?while usage can help us until the fact is proven. We need not stop using or ban them! (Just a caution to be exercised). This will help us in reduction of exposure and proper usage of the hair care product without harm and same time getting the purpose of cosmetic!

2.???Even though the study used several co-variates, due to limitations in availability of full extent of data, all co-variates are not evaluated at full fledge to understand the fact “Is hair straighteners cause of uterine cancer? or it is just an association, and the cause could be some other which is related to hair straightener”

3.???This epidemiological study knowing the vulnerable population would be black women, it looks like enough thought was not kept to include them in sufficient size, which provided an avenue for uncertainty to ascribe the study results to sensitive people. As per my knowledge roughly 13% of female population in US is African American for whom this study should help!

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Conclusion

What should a consumer or women who use straighteners should do after all above story!

Just take into the cognizance of this observation and be conscious while using hair straighteners, that could decrease the frequency of exposure until a concrete conclusion comes out. This is more relevant to black women in US based on the observations made in the study.

Please note this epidemiological study is just an observation in certain set of population. Can it be applied for all general population- No not yet!

At least, can we be cautious- Yes- we can!

No need to stop using hair straightener because the cause of uterine cancer due to hair straightener is still not yet established!

If you encounter any uterine cancer incidence with hair straightener alone, bring it to notice of NIEHS or interested parties- That will help them in their evaluation.

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Disclaimer: All views and opinions expressed in the article are those of the author (Dadisetti Pardeep) and they do not necessarily reflect or purport to reflect the opinions of any organization or company related to author. The author has neither personal interests nor conflict of interests with both NIEHS and people who believe NIEHS results could be false.?