A hair relaxer is a chemical treatment that permanently straightens curly or coily hair by breaking the internal bonds that give hair its natural curl pattern. Once applied, the straightening effect is permanent on the treated hair, though new growth will come in with your natural texture and need touch-ups every 8 to 10 weeks. Relaxers are most commonly used by Black women, and they remain one of the most popular chemical hair treatments worldwide.
How Relaxers Change Your Hair
Your hair’s curl pattern is determined by tiny chemical connections inside the hair shaft called disulfide bonds. These bonds act like the rungs of a ladder, holding your hair’s shape in place. A relaxer uses a strongly alkaline (high-pH) cream to break those bonds and then reform them in a straighter configuration. The result is hair that lies flat instead of curling.
This change happens at the structural level, which is why it’s permanent. It also means the process can’t be undone. Once those bonds are broken and reset, the only way to return to your natural texture is to grow out or cut off the relaxed hair. Relaxers also break down some of the protein structure in each strand, which is why treated hair loses tensile strength and becomes more fragile and prone to breakage than untreated hair.
Lye vs. No-Lye Relaxers
The two main types of relaxers are lye and no-lye formulas. Both are highly alkaline, but they use different active ingredients and have slightly different effects on the hair and scalp.
Lye relaxers use sodium hydroxide (also called caustic soda) as the active ingredient. About 63% of relaxers on the market fall into this category. They tend to process quickly and produce very smooth results. In lab testing, sodium hydroxide relaxers had median pH values around 12.36, with some adult formulas reaching as high as 13.17. For context, anything above a pH of about 11.5 is considered corrosive to skin.
No-lye relaxers typically come as a two-part system: a calcium hydroxide cream and a liquid activator. When you mix them together, they form a compound called guanidine hydroxide. Despite the gentler-sounding name, no-lye relaxers are actually more alkaline than lye versions. Testing found a median pH of 13.77 after mixing, rising to 13.82 after 24 hours. No-lye formulas tend to be less irritating to the scalp, which is why they’re often marketed for sensitive skin or home use. However, they can leave calcium deposits on the hair that make it feel dry or dull over time.
Children’s relaxer products tested in the same study were nearly as alkaline as adult versions, with lye-based children’s products reaching pH values of 12.82.
What Happens During Application
Whether done at a salon or at home, the basic process follows the same steps. A petroleum-based cream is applied to the scalp and hairline first to create a protective barrier against chemical burns. The relaxer cream is then applied section by section to new growth only, starting at the areas most resistant to straightening (usually the back of the head). Timing is critical. Leaving the product on too long causes excessive protein damage, while removing it too soon produces uneven results.
Once the desired level of straightening is reached, the relaxer is rinsed out thoroughly with water. A neutralizing shampoo follows, and this step is non-negotiable. The neutralizing shampoo brings your hair’s pH back down from that extreme alkaline level to its normal slightly acidic range. Most neutralizing shampoos contain a color indicator that changes (typically from pink to white) to show when all the chemical residue has been fully removed. Skipping or rushing this step can leave active chemicals on your scalp and hair, leading to continued damage.
Touch-Up Timing and the Line of Demarcation
Since relaxers only affect the hair that’s already grown out of the scalp, your natural texture will reappear at the roots as new hair grows in. Most stylists recommend touch-ups every 8 to 10 weeks, which gives you roughly half an inch to one inch of new growth for the relaxer to work with. You need enough regrowth to see a clear line where the relaxed hair ends and the natural texture begins.
Going too long between touch-ups creates a problem at the “line of demarcation,” the point where relaxed and natural hair meet. This junction is the weakest spot on the hair shaft because two very different textures are pulling against each other. When regrowth gets too long, the relaxer also has to stay on longer to process hair that’s farther from the warmth of the scalp, and that extra processing time weakens the strand further. On the other hand, people with faster-growing hair or very short styles like pixie cuts may need touch-ups closer to every 6 weeks. The key is to only apply relaxer to the new growth, never overlapping onto previously relaxed hair, which would cause double processing and severe breakage.
Caring for Relaxed Hair
Because relaxers permanently alter the protein structure of your hair, maintenance is built around two things: rebuilding strength and maintaining moisture. Think of it as a balance. Protein is the structure of your hair (it’s made primarily of the protein keratin), and moisture is what keeps it flexible. Too much protein without enough moisture leaves hair stiff and brittle. Too much moisture without protein makes it limp and stretchy to the point of snapping.
Regular protein treatments help reinforce strands that have been weakened by chemical processing, reducing breakage and shedding. Deep conditioning with moisture-rich products keeps chemically treated hair from becoming dry and fragile. Most stylists recommend alternating between protein and moisture treatments, adjusting the balance based on how your hair feels. If it snaps easily, it likely needs moisture. If it feels mushy or overly stretchy when wet, it needs protein.
Health Concerns Worth Knowing About
A 2022 study from the National Institutes of Health raised significant concerns about hair straightening chemicals and cancer risk. Researchers followed 33,497 women ages 35 to 74 for nearly 11 years as part of the Sister Study. Women who used hair straightening products frequently (more than four times in the previous year) were more than twice as likely to develop uterine cancer compared to women who didn’t use these products. Among women who never used straighteners, an estimated 1.64% would develop uterine cancer by age 70. For frequent users, that figure rose to 4.05%.
The concern extends beyond cancer risk. Lab analysis of hair products commonly used by Black women found 45 endocrine-disrupting or asthma-associated chemicals across the products tested, spanning every chemical class researchers looked for. Relaxers specifically contained nonylphenols, parabens, and fragrances at notable levels. Diethyl phthalate, a fragrance-related chemical classified as an endocrine disruptor, was the most frequently detected compound across all products tested. Endocrine disruptors interfere with your body’s hormone signaling, and long-term exposure through scalp absorption is an active area of concern.
How Relaxers Compare to Keratin Treatments
If you want smoother hair but aren’t sure about committing to a relaxer, keratin treatments work very differently. A relaxer breaks the bonds inside your hair and permanently reshapes them. A keratin treatment coats the outside of the hair shaft with a layer of protein, smoothing frizz and loosening curl without altering the internal structure. The results from a keratin treatment are temporary, typically lasting 3 to 5 months before fading gradually.
Because keratin treatments don’t break bonds, they’re less damaging to hair and don’t create the same line-of-demarcation problem that relaxers do. However, they won’t fully straighten very curly or coily hair the way a relaxer can. They’re better suited for reducing frizz and wave than for achieving bone-straight results. Some keratin treatments also contain formaldehyde or formaldehyde-releasing chemicals, so they carry their own set of health considerations.