In fact, hair dye users have significantly different levels of at least 11 metabolites circulating in their blood compared to those who don’t use it, according to research published in Scientific Reports.
What does that mean for your health? It’s hard to say for sure because there are no clinical trials that prove that one product or another increases risk. However, cohort and case-control studies have shown associations between hair dye use and some negative health outcomes.
A recent study review of 96 articles suggests that women who use permanent or semi-permanent hair dye just once or twice have a 7% increased risk of breast cancer, while those who use it 35 to 89 times have a 31% increased risk. Permanent dye was also associated with a 250% increased risk of bladder cancer in people with certain genetic factors.
“There can be health risks with using these chemicals, especially if you’re continually exposing your body to them over time,” says Maclin. “It’s a progression.”
Permanent dyes penetrate hair to its middle layer — the cortex — to strip existing pigment and leave new color behind. Semipermanent and temporary dyes tint the outer layers of the hair and wash out over time.
Researchers point to aromatic amines in permanent dyes, chemicals that help hair color stick to your strands, as potential culprits that might increase cancer risk. These substances can bind to DNA and lead to cancerous mutations. They can also affect reproductive health by mimicking or blocking the sex hormone estrogen.
A recent cohort study from Schildroth’s research group suggests that women who use hair dyes might have an increased risk of uterine fibroids, which are noncancerous growths that can cause pain or reduce fertility. Black women who used temporary hair color rinses the past 12 months had a 98% increased risk of fibroids.
“Fibroids are typically very responsive to estrogen, so if you have a chemical that mimics estrogen in the body, it could then, in turn, influence the way fibroids grow and develop in the body,” she says.
Schildroth also notes that temporary hair colors are usually thought to be safer than permanent dyes, since they contain fewer aromatic amines. However, her study’s results raise questions about their safety.
