Do Hair Straighteners Really Cause Cancer? New Research Revealed

The fact that women with wild waves, crazy-cool corkscrews and natural kinky textures often want sleek, straight hair means big business for salons. It also keeps us spending major money on products that allow us to straighten our own hair over the bathroom sink.

Well, here’s a heads up: A new study (a biggie, that followed more than 33,000 racially and ethnically diverse American women for over a decade) has found that, compared with people who never used them, women who frequently used chemical straightening processes and products had more than double the risk of uterine cancer.

“These findings are consistent with prior studies supporting a role of chemical straighteners in increased risk of other female, hormone-related cancers, the authors wrote in the Journal of the National Cancer Institute. (They found no uptick in uterine cancer associated with the other hair care products they looked at, which included various types of hair dyes, bleaching agents and perms.)

When researchers analyzed the data by race, they found that frequent straightener users of all races were equally likely to develop uterine cancer — but Black women comprised 60% of that group. “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,” said Che-Jung Chang, Ph.D., one of the study’s authors at the U.S. National Institute of Environmental Health Safety (NIEHS).

Whoa! What explains this link?

Researchers need to do more digging to know exactly, but it is clear that exposure to excess estrogen and imbalances in the hormones estrogen and progesterone are risk factors for uterine cancer. “When we say uterine cancer, most of the time what we mean is endometrial cancer, because 95% of uterine cancer starts in the endometrium, the lining of the uterus,” says Jamie N. Bakkum-Gamez, M.D., a professor of obstetrics and gynecology at the Mayo Clinic in Rochester, MD, who focuses on early detection and treatment of endometrial and ovarian cancers. “The hormone that stimulates the lining of the uterus is estrogen, and anything that pushes the balance more toward estrogen exposure can increase the risk of endometrial cancer.”

And some straightening products contain various chemicals known as endocrine disruptors, so called because they mess with the way hormones behave in our bodies. Endocrine disrupting chemicals, says Dr. Bakkum-Gamez, “can enhance that potential for a more estrogenic effect.” This is why they are thought to play a role in certain hormonal cancers.

There are also other potentially problematic chemicals in hair straightening products, too, says Birnur Aral, Ph.D., the executive director of the Beauty, Health & Sustainability Lab at the Good Housekeeping Institute. “Relaxers are thought to contain lye, a.k.a. sodium hydroxide, which is highly alkaline, to break the disulfide bonds in curly hair,” she says. And some other products, notably many keratin smoothing treatments, have been known to contain the carcinogen formaldehyde (or chemicals that when heated, as with a flat iron, turn into formaldehyde) the fumes of which clients — and stylists — then inhale. “Formaldehyde definitely volatilizes from the product and goes into the gas phase and thus can reenter body through eyes and mucous membranes during process,” says Aral.

Cosmetics aren’t approved by the FDA before they go on the market, but it is illegal to include chemicals that cause harm if used as directed. Nevertheless, it happens. In 2011, for example, the Good Housekeeping Institute experts found high levels of formaldehyde in several salon brands of smoothing treatments that claimed to be free of the carcinogen.

The study authors also note that chemicals might be absorbed more readily through the scalp than they would if applied to other areas of the body. But Crystal Ugochi Aguh, M.D., Associate Professor of Dermatology at Johns Hopkins School of Medicine and author of 90 Days to Beautiful Hair, posits that irritation to the scalp from harsh chemicals might be where the greater risk of skin penetration lies. “A treatment such as a keratin straightening treatment, which contains formaldehyde releasers, or chemical relaxer whose main ingredients could include sodium hydroxide (lye) or guanidine hydroxide (no-lye), could, if applied incorrectly, lead to scalp irritation and enhance systemic absorption,” she says. “But this has never been studied directly.”

The NIEHS scientists suspected there might be an association between chemical straighteners and uterine cancer because multiple studies have already linked hair straighteners and other hair products to a higher incidence of breast cancer; just a couple of years ago, this team’s research also found a link between straighteners and ovarian cancer.

There is already a lawsuit

Days after the release of the NIEHS study, Jenny Mitchell, a 32-year-old Missouri woman who had been using straightening products since the age of 10, filed a suit against five companies that manufacture the products she used, according to the Washington Post. Mitchell was diagnosed with uterine cancer in 2018, and had to have a hysterectomy; she’s asking for monetary damages and for the companies to pay for medical monitoring, and her attorney said there would likely be more such lawsuits in the future.

“Mitchell, who is Black, accuses L’Oreal of deliberately marketing its hair-straightening products to Black women and girls and failed to warn of risks, despite knowing since at least 2015 that they contained potentially dangerous chemicals,” Reuters reported.

For its part, L’Oreal, which is the parent company for one of the products Mitchell says she used, said in the Post that it has confidence in its products and that they’ve been rigorously evaluated by for safety. They also pointed out that the study does not find a direct causal link between cancer and hair straighteners.

The pressure to go straight

Black women in particular have faced decades of pressure to have hair deemed to be “appropriate for a professional setting,” which is to say, aligning with mainstream white beauty standards. While the natural hair movement has been gaining steam — and earlier this year the House of Representatives passed The Crown Act, which aims to protect people who wear natural hairstyles against discrimination — conscious and unconscious biases still cause harm.

Recent research conducted at Duke University recruited volunteers of different races to act as HR professionals. It found that Black women candidates with natural hairstyles received lower scores on professionalism and competence, and were not recommended as frequently for interviews compared with three other types of candidates: Black women with straightened hair and white women with curly or straight hair, the researchers found.

“These conformity pressures manifest as an expectation that hair should be worn as long and straight as opposed to the natural way from which the hair grows from the scalp for most Black women,” says Ashleigh S. Rosette, Ph.D., Senior Associate Dean, Executive Programs, at Duke’s Fuqua School of Business, a co-author of the study. “Given the negative health consequences that have been shown to be associated with chemically straightening their hair, Black women may face a precarious dilemma — a choice between their health and their financial livelihood.”

Mitchell herself cited this pressure to conform as part of the reason she used chemical straighteners starting at age 10. As she told the Washington Post, she felt her hair must “look a certain way, lay a certain way, flow a certain way in order to look professional” and “fit in.”

I’ve chemically straightened my hair! How worried should I be?

Before you freak out, some perspective: Uterine cancer, while, the most common gynecologic cancer in the U.S., is pretty rare overall, so even a doubling of the risk (1.6% as opposed to around 4%, according to the study) doesn’t make it likely. And the NIEHS study only shows an association, not that straighteners cause cancer.

Also key: Participants were recruited between 2003 and 2009, and they were merely asked about ‘straighteners.’ “We did not distinguish between at-home or in-salon treatments for straighteners [and] relaxers,” lead investigator Dr. Alexandra White told Good Housekeeping. That means the study’s findings may not apply across the board to all products marketed as straighteners, or all products available currently, she says.

In other words, different types of products — all of which could be considered straighteners — have different ingredients, and the study didn’t examine each of these chemicals separately. That’s why, says Dr. Aguh, it’s hard to know without further research which ones are potentially harmful.

Lastly, the researchers defined “frequent” use of chemical straighteners as more than four times in the year prior to signing up for the study. Participants who used them less often had some increased risk for uterine cancer, but not enough to make it statistically significant.

Do Black women need to be especially careful?

Black women are thought to use chemical straighteners more and tend to start younger, so any downside to these products has the potential to affect heavy users more.

Add to that that uterine cancer seems to be on the rise in general, especially among Black women. And, like some other cancers, uterine cancer is more deadly for Black women: Black women die of uterine cancer at twice the rate of white women, a recent report from the American College of Obstetrics and Gynecologists stated.

There appear to be many reasons for this, including racial inequities in healthcare that often lead to Black women being diagnosed later, as well as the fact that Black women are more likely to develop a more aggressive form of uterine cancer. “One thing that has been shown is that Black women seem to be twice has likely to have one of those more aggressive histologies diagnosed,” says Dr. Bakkum-Gamez, but neither that, nor being diagnosed later entirely explains why Black women fare worse. “We don’t fully understand all of the complexities that go into it. This is an area of very active research,” the fruits of which will hopefully save women’s lives.

But this single study — while helpful in that it prompts us to ask more questions about what’s in the products we use — does not offer enough information to make a recommendation, says Dr. Aguh. “The only thing linking these products [in the study] are the fact that they turn hair from curly (or wavy) to straight,” she says. The study did not point to a particular chemical, she says, and so more research is needed.

So what should you do?

That depends on how badly you want straighter hair, and how much you care about your straight hair being long-lasting and fuss-free. You’ll want to balance the look and the convenience against your concern about uterine and other kinds of cancer, which may also have to do with your unique risk factors.

Some of these risk factors include:

• Carrying a lot of body fat. “Peripheral fat stores are a source of excess estrogen, and obesity alone doubles the lifetime risk of endometrial cancer,” says Dr. Bakkum-Gamez. That’s not to say that it’s always within your power to change your weight, but because fat cells produce estrogen, carrying more weight increases your risk.
• Having diabetes. Type 2 diabetes is associated with being overweight, but the risk of endometrial cancer remains higher in people of lower weight with Type 1 diabetes as well, she says.
• Hypertension
• A family history of certain cancers, including colon and ovarian cancers. This could be a sign of a genetic disorder called Lynch syndrome, which ups your risk of uterine and other cancers, says Dr. Bakkum-Gomez.

Reducing your risk:

Here are a few options to consider if you want a straight look but are concerned about health risks of chemical straighteners:

• Straighten less often. The strongest association between chemical straighteners and uterine cancer was among frequent users (women who had straightened their hair with chemicals more than four times in the year before the study began). The increase in risk among people who used straighteners less frequently was much lower. So one option would be wait until you feel you absolutely must straighten again — it’s also better for your hair and scalp, says Dr. Aguh. “Decreasing the frequency of chemical treatment will be helpful to the overall health of the hair and that is an easy place to start,” she says.
• Find a trustworthy salon. “Generally speaking, I always recommend that women pursue chemical treatment with a professional only,” says Dr. Aguh. “This minimizes the risk of these products coming into contact with the scalp and leading to subsequent scalp irritation.” That also means not trying to chemically straighten your hair by yourself at home. If you choose to go to a salon, look for one with good ventilation, says Aral, especially if your treatment includes chemicals that emit potentially dangerous fumes. And don’t be afraid to ask questions about what is in the straighteners your stylist is using.
• Pick products that have been vetted and judged to be relatively safe. For example, in 2015, the Good Housekeeping Beauty Lab looked at some keratin smoothing offerings that came out after its 2011 investigation that discovered undisclosed formaldehyde, and found them to be free of the carcinogen or containing it but at levels considered to be safe.
• Skip chemical straighteners altogether. The safest thing is to rock your natural hair, or if you really want to go straighter, the Good Housekeeping Beauty Lab advises reliance on solutions that are based on heat styling and products that will set hair temporarily. These include defrizz products and heat tools such as flat irons, curling irons, straightening brushes and blow dry brushes. “This way the worst that can happen is that you may have hair damage — which you likely get with overdoing straighteners and relaxers anyhow — but you don’t get exposed to strong chemicals like acids, bases and formaldehyde that can seep through their skin or inhale fumes,” says Aral.

What are the warning signs of uterine cancer?

Uterine cancer is very treatable if it’s found early, says Dr. Bakkum-Gamaz. Whether or not you use chemical hair straighteners, it’s always a good idea to be aware of the early warning signs of uterine cancer:

• Pelvic pain or pressure. Pain in your pelvic area can be many things, most of which are not serious, but it’s still a good idea to get checked out, especially if you’re also bleeding.
• Painful urination or intercourse.
• Abnormal bleeding, spotting or discharge.

Abnormal bleeding is the biggie, says Dr. Bakkum-Gamaz. “Ninety percent of people diagnosed with endometrial cancer will have had some kind of abnormal bleeding,” she says. Don’t panic: Only 5-10% of people with abnormal bleeding will have any type of cancer, she adds. But since there is no screening test for uterine cancer, it’s critical to not blow off weird bleeding.

What does that mean, exactly? Any bleeding after menopause (even just spotting or a pink drop when you wipe) needs to be checked out, she says. “That’s a big red flag,” she says. Bleeding may be with or without pain.

And for women who are pre-menopausal or going through perimenopause, you’re looking for bleeding that is definitely not a period, she says. “If periods are spacing out but you’re not bleeding in between periods and are in the rough age of menopause, that’s very normal pattern,” says Dr. Bakkum-Gamez. “Periods can get lighter or heavier and that’s still a period.” But anything in between what could be a period, consistent bleeding or if you’re not sure your bleeding is a period, you should get checked, she says.