Perms have not been shown to cause cancer. The main chemical in perm solutions, ammonium thioglycolate, has been tested for carcinogenicity and showed no evidence of causing cancer in safety assessments. That said, the picture gets more complicated when you look at related hair treatments, occupational exposure for salon workers, and certain chemicals that overlap between products.
What’s Actually in a Perm Solution
Traditional perms use thioglycolate compounds to break and reform the bonds in your hair, changing its shape. A comprehensive safety review of ammonium thioglycolate and related compounds found they were not mutagenic (meaning they don’t damage DNA) and showed no evidence of carcinogenicity. The review did note that thioglycolates can irritate skin and eyes, and some people develop sensitivities to them, but cancer was not among the identified risks.
Your skin does absorb some of these chemicals during application. Research shows that thioglycolate compounds are water-soluble and penetrate the skin readily. After a single application, 5% to 8% of the absorbed dose is excreted in urine within an hour, and 30% to 50% within five hours. So the body processes and clears these compounds relatively quickly.
Perms vs. Straighteners: An Important Distinction
Much of the cancer concern around hair treatments actually comes from research on chemical hair straighteners and relaxers, which are different products with different ingredients. This distinction matters because the two are often lumped together in headlines.
A major NIH-funded study found that women who frequently used hair straightening products (more than four times a year) were more than twice as likely to develop uterine cancer compared to women who didn’t use them. To put that in perspective: about 1.64% of women who never used straighteners would develop uterine cancer by age 70, compared to 4.05% of frequent users. That’s a meaningful jump, but it applies to straightening chemicals, not traditional perm solutions.
Some hair straightening and smoothing products contain or release formaldehyde when heated. The FDA has moved toward banning formaldehyde in these products. Traditional cold-wave perms don’t involve the same heating process and don’t typically contain formaldehyde. If you’re looking at product labels, watch for the terms “formalin” and “methylene glycol,” which are alternate names for formaldehyde-related ingredients.
What the Breast Cancer Research Shows
The Sister Study, a large NIH investigation tracking over 50,000 women, looked specifically at whether using perms during adolescence (ages 10 to 13) affected breast cancer risk later in life. Over about 10 years of follow-up, 3,380 women developed breast cancer. The results for perms were largely reassuring.
Women who sometimes used perms as adolescents had essentially no increased risk of breast cancer overall. Frequent perm use showed a modest, statistically nonsignificant increase in risk for premenopausal breast cancer, but no increase for postmenopausal breast cancer. The trend across all usage levels wasn’t statistically significant either, meaning the pattern could easily be due to chance. By contrast, frequent use of hair straighteners in the same study was associated with a more notable doubling of premenopausal breast cancer risk.
The Risk Is Higher for Salon Workers
Where cancer risk does appear more clearly is among hairdressers who spend years exposed to a cocktail of salon chemicals daily. A meta-analysis of 42 studies found that hairdressers had a 34% higher risk of bladder cancer compared to the general population. That risk climbed with time on the job: hairdressers who worked in the profession for 10 years or more had a 70% increased risk.
Male hairdressers showed a somewhat higher risk (52% increase) than female hairdressers (25% increase), though the reasons aren’t entirely clear. Importantly, this elevated risk persisted even after accounting for smoking, which is the biggest known risk factor for bladder cancer. The exposure here isn’t from a single chemical but from decades of daily contact with dyes, bleaches, perm solutions, and straightening products combined.
For someone getting a perm a few times a year, the exposure is orders of magnitude lower than what a full-time stylist experiences over a career.
How to Think About Your Personal Risk
The American Cancer Society’s current position on hair treatments is cautious but not alarming. The organization notes that most studies have not found a strong link between personal hair product use and cancer, though more research is needed. They don’t issue specific warnings against perms or recommend that current or former users take any particular medical steps beyond standard screening.
If you’re weighing the risks, the practical takeaway is that traditional perms using thioglycolate-based solutions carry far less concern than chemical hair straighteners or relaxers, which contain different and more worrisome compounds. The frequency of use also matters. Occasional treatments expose you to much less than regular use over many years. And if you do use multiple chemical treatments, spacing them apart reduces the chemical load on your scalp at any one time. The ACS recommends waiting at least 14 days after perming before applying hair dye.