A chemical relaxer permanently straightens curly hair by breaking the protein bonds that give each strand its shape. Once those bonds are rearranged, the treated hair stays straight until new curly growth comes in at the roots. The change is irreversible on the strands that have been processed, which is why understanding exactly what’s happening inside your hair matters before you sit down in the chair.
How a Relaxer Changes Hair From the Inside
Your hair’s curl pattern comes from disulfide bonds, which are strong sulfur-to-sulfur links between the keratin proteins that make up each strand. Think of these bonds as tiny bridges holding your hair’s coiled shape in place. A relaxer’s job is to break those bridges so the strand can be reshaped.
The active ingredient in most relaxers is an alkaline chemical, typically sodium hydroxide (found in about 63% of products on the market) or calcium hydroxide or lithium hydroxide in “no-lye” formulas. All of them work at an extremely high pH, with a median around 12.4. For context, pure water sits at 7 and household bleach is around 12.5, so these products are genuinely corrosive.
At that pH, the hydroxyl ions penetrate the outer cuticle layer and reach the cortex, the structural core of the strand. There, they break apart the disulfide bonds in a process called lanthionization. Sulfur atoms are released (which is why you may notice a distinct sulfur smell during application), and a new amino acid called lanthionine forms. While the bonds are broken, the hair becomes soft and malleable. A stylist then physically smooths and stretches the strand into a straight position, and the bonds reform in that new configuration.
Why the Neutralizing Step Matters
Rinsing out the relaxer doesn’t finish the job. The bonds inside your hair are still actively reforming as the pH drops, so how the strand is positioned during this window determines its final shape. If hair is handled roughly, bunched up, or left to curl while the crosslinks are still setting, the result can look wavy or under-processed.
A neutralizing shampoo, typically with a pH between 5.5 and 7, is applied immediately after rinsing to bring the hair into an acidic range and lock the bonds into place permanently. Research on the chemistry of this step shows that the most efficient reconfiguration happens below a pH of about 5. Skipping or rushing the neutralizer is one of the most common reasons a relaxer doesn’t deliver fully straight results.
Choosing the Right Strength
Relaxers come in three strengths: mild (or fine), regular, and super. The distinction is about the thickness and resilience of individual strands, not how much hair you have on your head. Fine strands need the mildest formula. Medium-textured strands pair with regular strength. Coarse, resistant strands typically require the super formula.
A common mistake is assuming that thick, dense hair needs a super-strength product. You can have a full head of hair with individually fine strands, and using too strong a formula on those strands will cause serious damage. If you’re unsure, a stylist can assess your strand diameter before you commit.
What Happens to Hair Over Time
Because lanthionization is a one-way chemical reaction, the straightened portions of your hair will never revert to their original curl pattern. New growth, however, comes in with your natural texture. This creates a visible line of demarcation between the straight processed ends and the curly roots, which is why touch-ups become necessary.
The standard recommendation is to wait 6 to 8 weeks between touch-ups, though some people stretch to 10 or 12 weeks. Applying relaxer too soon overlaps the chemical onto already-processed hair, which weakens it progressively. Over-processed hair loses elasticity, becomes brittle, and breaks easily. Touch-ups should only target the new growth, not the entire length of the strand.
Scalp and Skin Risks
Products with a pH above 12 are classified as corrosive to skin, and relaxers marketed for children tested at the same pH levels as adult formulas. During application, the most common complaints are throbbing pain, tingling, burning sensations, and redness. In mild cases, this resolves quickly. In more serious cases, blisters form, followed by peeling and inflammation.
Scratching your scalp, brushing aggressively, or washing your hair in the days before a relaxer appointment creates micro-abrasions that let the chemical penetrate skin more easily. Most stylists advise leaving the scalp undisturbed for at least a few days beforehand and applying a petroleum-based protectant along the hairline and scalp before the relaxer goes on.
Long-Term Health Concerns
Beyond immediate scalp irritation, longer-term health effects have drawn increasing attention. The Black Women’s Health Study followed nearly 45,000 Black women over 22 years and found that postmenopausal women who used relaxers heavily (15 or more years, at least five times a year) had a 64% higher risk of uterine cancer compared to women who never used them or used them infrequently. Among premenopausal women, no elevated risk was detected. A separate study, the Sister Study, found an even stronger association: women who used relaxers more than four times in the prior year had roughly 2.5 times the risk of uterine cancer compared to non-users.
These findings don’t prove that relaxers directly cause cancer, but the association is strong enough that many researchers point to endocrine-disrupting chemicals found in some relaxer formulations as a plausible mechanism. It’s worth factoring into your decision, especially with long-term, frequent use.
How Relaxers Differ From Keratin Treatments
Relaxers and keratin treatments both aim to reduce curl and frizz, but they work in fundamentally different ways. A relaxer breaks the disulfide bonds inside the cortex and permanently restructures them. A keratin treatment coats the outside of the hair cuticle with protein and conditioning agents, sealed in with heat. It smooths and loosens curl without altering the internal bond structure.
The practical difference: a relaxer makes hair permanently straight until it grows out. A keratin treatment is semi-permanent, gradually fading over several weeks to months, and your original curl pattern returns fully. Keratin treatments reduce frizz and improve manageability without committing you to a completely different texture. Relaxers give you a dramatic, lasting change but require ongoing chemical maintenance and carry a higher risk of damage.
If you want to soften your curl pattern rather than eliminate it entirely, a keratin treatment is the less invasive option. If you want bone-straight hair and are prepared for the upkeep, a relaxer delivers that result more completely.