Hair Relaxers and Cancer What the Research Really Says
The debate over hair relaxers and cancer is not just a beauty story. It sits at the intersection of science, personal choice, race, workplace bias, product safety, and trust.
For decades, chemical relaxers have been part of many hair care routines, especially for Black women and girls in the United States. They can make tightly curled or coiled hair straighter and easier to style in certain ways. They can also burn the scalp, damage hair, and expose users and stylists to strong chemicals.
In recent years, a new concern has moved to the center of the conversation: whether long-term use of chemical hair straighteners may be linked to certain cancers, especially hormone-related cancers such as uterine cancer and breast cancer.
The short answer is this: some studies have found associations between frequent use of chemical hair straighteners and higher risk of certain cancers, but the research does not prove that relaxers directly cause cancer. The details matter.
This article is for general information only and should not replace medical advice from a clinician.
Why this question is getting more attention
Concern about chemical hair straighteners has grown for several reasons.
Researchers have paid more attention to endocrine-disrupting chemicals, which are substances that may interfere with hormones. Some hair products have been found to contain ingredients or contaminants such as phthalates, parabens, bisphenols, metals, or formaldehyde-related compounds. Not every product contains the same chemicals, and labels do not always tell the full story.
At the same time, many people use these products repeatedly over many years. A single exposure is different from routine use that starts in childhood and continues into adulthood.
The issue has special weight in the Black community because chemical relaxers have historically been marketed heavily to Black women. Straight hair has also been treated, unfairly, as more “professional,” “neat,” or socially acceptable in schools and workplaces. That pressure can shape personal grooming choices long before anyone has a chance to weigh health risks.
So the question is not simply, “Are relaxers safe or unsafe?” A better question is: What does the evidence show, what does it not show, and how can people make informed choices now?
What traditional hair relaxers are and how they work
Traditional chemical relaxers permanently change the structure of hair.
Hair gets its shape partly from disulfide bonds, which help determine curl pattern. Relaxers break or rearrange those bonds so tightly curled hair becomes straighter. Once hair has been chemically relaxed, that treated section stays altered until it grows out or is cut.
Common types include:
Lye relaxers
These usually contain sodium hydroxide. They work quickly and can be harsh on the scalp if applied incorrectly.
No-lye relaxers
These often use calcium hydroxide with guanidine carbonate. They may be marketed as gentler, but they can still irritate the scalp and damage hair.
Thio relaxers
These use ammonium thioglycolate and are more common in some permanent waving or straightening systems.
The immediate risks of relaxers are well known. They can cause scalp burns, irritation, hair breakage, thinning, and chemical injury, especially when left on too long, applied to already irritated skin, or used too often.
The cancer question is more complex because it involves long-term disease risk, exposure over time, and chemicals that may affect hormones or inflammation.
Keratin treatments are not the same thing
Keratin treatments are often grouped with relaxers, but they are different.
A keratin treatment, sometimes called a Brazilian blowout or smoothing treatment, usually aims to reduce frizz and loosen curl for a limited time. It does not work the same way as a traditional hydroxide relaxer. Many keratin treatments coat the hair and use heat from a flat iron to seal the effect.
The main safety concern with some keratin treatments has been formaldehyde exposure or exposure to chemicals that release formaldehyde when heated. Formaldehyde is a known carcinogen in certain exposure settings, especially through inhalation over time. It can also irritate the eyes, nose, throat, and lungs.
This matters because the risk profile differs:
Traditional chemical relaxers | Keratin smoothing treatments |
Permanently alter the hair’s internal bonds | Temporarily smooth or loosen curl |
Often use high-pH chemicals such as sodium hydroxide or related systems | May use aldehydes or formaldehyde-releasing ingredients |
Main immediate risks include burns, irritation, and breakage | Main immediate risks often include fumes, eye irritation, and breathing symptoms |
Research often groups them under “straighteners” or “relaxers,” which can blur differences | Product formulas vary widely, and “formaldehyde-free” claims can be confusing |
When reading studies or headlines, this distinction matters. Some research asks about “chemical straighteners” broadly. That category may include different products with different ingredients.
What the key studies have found
Most research on hair straighteners and cancer is observational. That means researchers look for patterns in real people’s lives rather than assigning people to use or avoid a product.
Observational studies can reveal important signals. They cannot, by themselves, prove cause and effect.
The Sister Study and uterine cancer
One of the most discussed papers came from researchers using data from the Sister Study, a large National Institutes of Health research project that follows women in the United States who had a sister diagnosed with breast cancer.
In a 2022 study, researchers reported that women who used hair straightening products frequently had a higher risk of developing uterine cancer than women who did not report using them. The study received wide attention because uterine cancer is a hormone-sensitive cancer, and because chemical straighteners may contain endocrine-disrupting substances.
A key point often missed in headlines is the difference between relative risk and absolute risk.
A study may report that risk is “more than doubled” in a group. That sounds alarming, but the absolute risk may still be relatively low for any one person. In the Sister Study analysis, the estimated risk by age 70 was still a minority of users, but it was higher among frequent users than non-users.
That does not make the finding unimportant. Uterine cancer rates and outcomes already show racial disparities in the United States, with Black women facing higher mortality. If a widely used product contributes even a small added risk across a large population, the public health impact could matter.
Breast cancer research
Several studies have also examined hair dyes and chemical straighteners in relation to breast cancer.
Research using Sister Study data found associations between some hair product use and breast cancer risk. One widely cited analysis reported that frequent use of chemical straighteners was associated with a higher breast cancer risk, and permanent hair dye findings varied by race and product type.
Other studies have produced mixed results. Some find links, some find weaker links, and some do not find clear associations after researchers adjust for other risk factors.
This does not mean the science is useless. It means the topic is hard to study. Breast cancer has many risk factors, including age, genetics, reproductive history, alcohol use, body weight after menopause, hormone therapy, and environmental exposures. Hair product use is one piece of a much larger picture.
Ovarian and other hormone-related cancers
Researchers have also explored whether hair straighteners may be connected to ovarian cancer and other hormone-related conditions. The evidence is still developing and less settled than many headlines suggest.
The biological concern makes sense. Some chemicals found in personal care products can act like hormones or interfere with hormone pathways in lab studies. But showing that a product changes cancer risk in people requires stronger and more consistent evidence.
Right now, the most responsible summary is this: the research raises concern, especially for frequent and long-term users, but it has not established a direct causal link for every product or every cancer type.
Why the studies are difficult to interpret
The science is not as simple as comparing “relaxer users” with “non-users.”
Here are some of the major challenges.
Product formulas are not all the same
Two boxes labeled as relaxers may contain different ingredients. Salon products may differ from at-home kits. Older formulas may differ from current ones.
Researchers often do not have the exact product name, ingredient list, batch, or application method for every participant over many years.
Use patterns vary
Cancer risk, if there is one, may depend on:
How often the product is used
Age at first use
Number of years used
Whether the product touches the scalp
Whether the scalp is burned, scratched, or irritated
Whether gloves, ventilation, or professional application are used
Whether other chemical hair products are used at the same time
A person who relaxed their hair twice in adulthood is not in the same exposure category as someone who started in childhood and used products every six to eight weeks for decades.
Ingredients may be hidden or incomplete
Personal care product labels can be hard to interpret. Fragrance mixtures, preservatives, contaminants, and heat-activated chemicals may not be obvious to consumers.
Some products marketed as “natural,” “gentle,” or “formaldehyde-free” can still contain irritating or concerning substances.
Social factors matter
Hair choices do not happen in a vacuum. School dress codes, workplace expectations, military grooming rules, media standards, and discrimination against natural Black hair have all influenced product use.
That history matters because it affects who was exposed, how often, and starting at what age.
Common misconceptions about relaxers and cancer
The public conversation often swings between panic and dismissal. Both can be misleading.
Misconception one says every relaxer causes cancer
The evidence does not support that claim.
Studies have found associations, especially among frequent users of chemical straightening products. They have not proven that every relaxer causes cancer in every person who uses one.
Cancer develops through many factors over time. Genetics, environment, hormones, age, health history, and chance can all play a role.
Misconception two says no proof means no risk
This is also wrong.
Lack of final proof does not mean a product is risk-free. Many public health decisions involve acting on concerning evidence before every answer is settled.
If a person decides to reduce or stop using chemical straighteners because of the research, that is a reasonable choice.
Misconception three says keratin treatments are automatically safer
Not necessarily.
Keratin treatments may avoid some of the chemistry of traditional relaxers, but some raise concerns about fumes and formaldehyde exposure, especially when heat is used. Stylists may face repeated exposure in salons, which is a different risk situation from occasional consumer use.
Misconception four says this is only about vanity
Hair is personal, cultural, and practical. For many Black women, straightening hair has been tied to acceptance, employment, safety, and social pressure.
Framing the issue as vanity ignores the discrimination that has shaped grooming choices for generations.
What consumers can do now
A balanced view does not require panic. It does call for awareness.
People who use or are considering relaxers can take practical steps to reduce exposure and make better-informed decisions.
Use less often if possible
Longer gaps between applications can reduce repeated exposure and may lower the chance of scalp irritation.
Avoid applying relaxer to broken or irritated skin
Cuts, scratches, burns, or inflammation may increase absorption and injury risk.
Do not leave products on longer than directed
Longer processing does not mean better results. It can increase burns and damage.
Ask about ingredients
For salon services, ask what product is being used and whether a safety data sheet is available.
Improve ventilation
This matters most for treatments that release fumes, including some smoothing and keratin services.
Consider alternatives
Heat styling, blowouts, twist-outs, braids, wigs, locs, silk presses, and natural styles all have their own maintenance needs and risks, but they may reduce chemical exposure.
Talk with a clinician about personal risk
This is especially useful for people with abnormal uterine bleeding, a strong family history of hormone-related cancers, or other risk factors.
One symptom deserves special attention: abnormal vaginal bleeding, especially after menopause. That does not mean cancer is present, but it should be evaluated.
The Black community deserves better than blame
The burden of this issue should not fall only on individual consumers.
For years, Black women and girls have received the message that their natural hair is less acceptable. That message came from schools, employers, media, and beauty standards. Many people used relaxers because straight hair made life easier in a society that punished natural texture.
Recent laws such as the CROWN Act, passed in several states and cities, aim to reduce discrimination based on natural hair texture and protective styles. That kind of policy matters because health choices become more meaningful when people are not penalized for making them.
Product makers also have responsibilities. Consumers should not need a chemistry degree to understand what they are putting on their scalp. Clear labeling, safer formulas, better testing, and honest marketing are basic expectations.
Researchers have responsibilities too. Studies should include diverse populations, measure exposure carefully, and separate product categories when possible. The phrase “hair straightener” is often too broad to answer the questions people actually have.
What the research really says
The current evidence points to concern, not certainty.
Frequent, long-term use of chemical hair straightening products has been associated in some studies with higher risk of certain cancers, especially uterine cancer. Breast cancer findings also raise questions, though results vary. Keratin treatments are different from traditional relaxers, but they are not automatically risk-free because some may involve formaldehyde-related exposure.
The most reasonable takeaway is not fear. It is informed caution.
If a relaxer is part of your routine, the science does not say you need to panic. It does support asking better questions, reducing unnecessary exposure when possible, watching for symptoms, and choosing products and stylists carefully.
The bigger lesson is that beauty products should be safe, labels should be clear, and no one should have to choose between cultural acceptance and health.
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