This one caught my attention.
In 2015 my (now ex) girlfriend was diagnosed with TNBC. I obviously researched the hell out of it to gain as much of an understanding as I possibly could as a non-medical professional as I'm sure anyone would, and most of my reading suggested that it was mostly African American women and youngish white ladies who tend to get this.
As far as I know, she had used permanent die at least once in her early twenties. Thankfully less than a year later and after chemo and surgery, she fully recovered.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7783321/
Edit: added space after comma, fixed grammo
The paper cites endocrine disruption, but that seems like the least of your worries.
Dyes have electron delocalization. That's why they're optically active. Those bonds will gladly participate in chemical reactions within your body. (One of the cited chemicals was a biphenyl, and looked particularly nasty.)
Chemical straightener is even worse. They're intended to break disulfide bonds, which are of critical importance in biochemical structure.
This stuff could percolate to your DNA and introduce deleterious changes.
I've used my fair share of dyes since my blue haired teenage years and I'm curious as they mention non-professional applications of dye in terms of risk. Does this mean the risk is elevated during the application phase and not the 'wearing' phase of dye use?
>We observed a higher breast cancer risk associated with any straightener use and personal use of permanent dye
This theory was quite popular in manosphere. Some hardcore haters were even making videos to warn women. If you check sources, studies like this go back to 1970ties. It will be interesting to see, if it gains traction now.
From a quick scan the results are a bit surprising. One should know that dying ones hair involves 2 components:
1. developer. Some liquid that breaks open your hair follicles, containing usually 3%/6%/9% hydrogen peroxide. This is the aggressive stuf.
2. hair dye. The stuff that contains the color pigments.
The more you have to bleach the hair, the more aggressive the developer formulation needs to be. If you have perfectly black hair and you want to go blond, you basically going for the nucleair scenario: aggressively breaking open your hair follicles so that the existing dark pigments will fall out of it (bleach) so that the new pigments can enter eventually.
It suggests that black women have higher risks than white women. But also that semi-permanent dyes do incur way less risk. Semi-permanent dyes work different as in that the developer is way less aggressive, as a trade of with doing a less thorough job in getting the hair follicles to open.
The strange this is that for black women, the color of the permanent dye makes a more drastic difference in cancer risk compared to white women.
"The association with permanent dye use among black women was evident for both dark-colored dye (HR = 1.51, 95% CI: 1.12–2.05) and, although less precise, light-colored dye (HR = 1.46, 95% CI 0.91–2.34). Among white women, breast cancer risk was associated with use of light-colored permanent dye (HR = 1.12, 95% 1.01–1.23) but not dark dye (HR = 1.04, 95% 0.94–1.16)."
For me, this leaves the question open if one is comparing apples with apples, as I don't see the formulation for the developer accounted for.