
Breast Cancer Linked to Permanent Hair Dye and Chemical Hair Straighteners - goshx
https://www.newsweek.com/breast-cancer-linked-permanent-hair-dye-chemical-hair-straighteners-study-almost-50000-women-1475328
======
modeless
> 7% higher risk in white women (HR = 1.07, 95% CI: 0.99–1.16)

The confidence interval _clearly_ includes 1.0. I'm tired of all these studies
being uncritically reported on in the press with no mention of the giant error
bars.

IMO medical researchers need to raise their standards. 95% is way too low.
Also, journalists should be ashamed at the state of science and medical
reporting. It's ironic that you can read articles blaming tech for the spread
of fake news and then turn the page to the health section and read garbage
like this article.

~~~
rand_r
Here’s a question I had when I learned this stuff in stats class: What does a
95% confidence interval actually mean? I could never get a clear answer.

~~~
bonoboTP
Not sure if the answer will be _clear_ , but that's inherent in the weird and
counter-intuitive nature of the concept itself (which I consider as a major
disadvantage of it).

It is an interval that was obtained using a confidence interval generation
procedure, for which the following is true: for any true value of the quantity
you're estimating, the procedure yields an interval that contains that correct
value 95% of the times, when run on different random samples collected
conditioned on that true value.

You want to estimate some quantity, let's say the cancer risk ratio of hair-
dyers to non-hair dyers. You make some (noisy) experimental measurements on
people.

Then, let's say someone hands you a _confidence interval generating
procedure_. You feed it with your measurement data and it spits out an
interval. To claim that this interval is a 95% confidence interval is
_actually_ a claim about the confidence interval generating procedure, not
about the particular interval. And that claim is that for any true cancer risk
ratio value, if we ran lots of experiments and fed all the results to this
procedure, then 95% of the resulting intervals would contain the correct
corresponding value. So in more detail: Assume the true ratio is, say, 1.05.
Then if we repeated our noisy experiment in a 1.05-ratio world and applied the
confidence interval generating procedure to the results, we would expect to
get 95% of those intervals containing the number 1.05 and 5% of them not
containing it. If we assume the ratio is 1.2, the same thing should hold. For
this analysis to work, we need an idealized measurement model that tells us
what the distribution of measurements looks like given any particular
underlying value of the quantity of interest (say the cancer ratio). Then
using this model and the description of a given confidence interval generating
procedure, we may be able to prove mathematically that it indeed has the above
property. Most of the time, statisticians use standards procedures, for which
this property has been proved and the proof is widely known. They rarely
invent new such procedures.

So, in summary: we don't know what the true value is in reality. But we can
prove that the confidence interval generating procedure has the above
explained property. Then, we will call the interval that this procedure gives
us on our real measurement data a 95% confidence interval.

What it definitely does _not_ mean is that the true value is in the interval
with 95% probability, and that's the most common misunderstanding.

I'm not sure if this helps at all. These things are really counter-intuitive
and twisted against our natural way of thinking.

~~~
rand_r
Framing it as statement about an interval generating procedure is really
interesting! Do you know what an example would be? Appreciate anything you can
point me towards to learn more.

Honestly, I feel like the whole concept is straight up weird and fascinating.

~~~
bonoboTP
This is an in-depth explanation (may take some time to digest it):

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4742505/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4742505/)

~~~
rand_r
Thank you.

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perspective1
It's a plausible mechanism but a bogus study. With most of their confidence
intervals including hazard ratios of 1.0 (or very close to it), they need to
rule out even slight correlations like smoking and (low) income. Recall bias
of the survey participants is another major factor in cancer cases. Overall
this reads like they collected data of a bunch of chemical exposures setting
their p to < 0.05 and found this one that they could publish on.

~~~
carlmr
>need to rule out even slight correlations like smoking and (low) income.

Especially with hair dying, since looking at my environment at least early
usage (before graying) is very much correlated with low income/education.

~~~
romdev
I'd like to see antiperspirant usage as a variable, but it seems like it would
be hard to find a control. Having tried several times to buy deodorant without
antiperspirant for my wife, I can say how hard it is to find an armpit product
without aluminum oxide. It's not so hard to find masculine scented deodorants.

~~~
carlmr
Yeah, I'm wondering why we're not erring on the side of caution there and
banning them until proven safe.

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btilly
I am glad that they have statistical evidence, however it has been believed
for a long time.

Beauty salons use a wide variety of products that are biologically active and
unregulated. Many are known carcinogens, and working at a beauty salon puts
you at increased risk of cancer. See
[https://www.ncbi.nlm.nih.gov/pubmed/19755396](https://www.ncbi.nlm.nih.gov/pubmed/19755396)
for random verification.

The question is what it does to the customers. It has long been suspected that
increased cancer rates among blacks are tied to the fact that they are more
likely to use beauty salons than whites. And if they do use them, they use
them more often.

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nostromo
Silly question: did they control for age?

Please tell me they did, because, duh... older women have more cancer and dye
their hair more.

I don't have access to the full paper, but the abstract makes no mention of
this, and states they included women from 35-74.

~~~
mmmrtl
Fortunately, yes

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velcrovan
> “The research was based on the medical records of more than 46,000 women
> aged 35 to 74 from the Sister Study, meaning all women involved had a close
> relative who had died of breast cancer.”

Can someone explain to me how this isn’t a huge problem for this study?

~~~
UnFleshedOne
If you want to be careful, you can say the study found that among cohort with
increased cancer risk due to genetics, using those hair products increased
cancer risk even further.

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thdrdt
The most important part of the article:

"While the paper is based on patterns and trends and, as such, doesn't confirm
a direct cause, ..."

Please be carefull jumping into conclusions. Further research is needed for
that.

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tropo
The only thing surprising here is that it isn't scalp cancer.

Hair straighteners work by breaking and reforming the disulphide bonds in
proteins. Proteins perform many important roles related to DNA repair,
chromosome formation, DNA replication, and other cancer-relevant actions. It
can't be good to have bonds in those proteins getting changed somewhat
randomly.

~~~
dsfyu404ed
Skin has millions of years of incremental improvement at keeping stuff out. It
is not unheard of for a carcinogen applied to the body to not cause skin
cancer directly but to cause cancer elsewhere because being on the body makes
it likely to get in through the various holes where it then finds its way to
some more susceptible tissue.

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tptacek
Is there a source for this that isn't Newsweek? Newsweek isn't really a
trustworthy source; they are, as I understand it, a publication several tiers
below Buzzfeed (which does good work sometimes) that has acquired and turned
Newsweek into a Newsweek Suit, Buffalo-Bill-style, and wears it around the
Internet.

~~~
clumsysmurf
[https://medicalxpress.com/news/2019-12-permanent-hair-dye-
st...](https://medicalxpress.com/news/2019-12-permanent-hair-dye-
straighteners-breast.html)

~~~
tptacek
Thanks!

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nbrempel
Direct link to the research article:
[https://onlinelibrary.wiley.com/doi/abs/10.1002/ijc.32738](https://onlinelibrary.wiley.com/doi/abs/10.1002/ijc.32738)

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pithymaxim
Slide summary from the authors: [https://bcerp.org/wp-
content/uploads/Session3-AlexandraWhite...](https://bcerp.org/wp-
content/uploads/Session3-AlexandraWhite_hair-dye-and-straightener-use-and-bc-
BCERP.pdf)

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Animats
Breast cancer, but not head skin cancer?

~~~
notacoward
Just guessing here, but I suppose it's because the effect has less to do with
where the chemicals get into the body than where they accumulate and/or have
an effect. As it turns out, scalp tissue is not sensitive to those chemicals
but breast tissue is. Could have been the liver or the prostate instead, but
it wasn't.

~~~
elliekelly
And if a woman has long hair at least some of the chemicals from the hair dye
will wash off over their breasts when they shower.

Also guessing here, but home hair dye is usually quickly washed off in the
sink while a salon will not only wash your hair more thoroughly but they tend
to wash it twice after dying. So I would assume that when a person showers
after home hair dye a lot more of the chemicals are rinsed off over their
breasts when compared to after a salon dye.

