Hair relaxer is a chemical treatment used to permanently straighten curly, coily, or tightly textured hair. It works by breaking the structural bonds inside each hair strand and reforming them in a straighter configuration. The result lasts until new hair grows in, which is why most people schedule touch-up treatments every 6 to 8 weeks. Relaxers are one of the most popular chemical hair treatments worldwide, but they require careful application and ongoing maintenance to avoid damage.
How Relaxers Straighten Hair
Your hair gets its natural shape from disulfide bonds, which are strong chemical links between protein chains inside the hair shaft. Curly and coily hair has these bonds arranged in a pattern that creates curves. A relaxer breaks those bonds using a highly alkaline cream, which allows the hair to be smoothed into a straight position. Once the hair is straight, a neutralizing solution (typically containing hydrogen peroxide) reforms the bonds in their new configuration. The straightening is permanent for the treated section of hair, but any new growth from the root will come in with your natural texture.
This is the same basic chemistry behind perms, just in reverse. Where a perm wraps hair around rods to create curls before resetting the bonds, a relaxer smooths the hair flat before locking it in place.
Lye vs. No-Lye Relaxers
Relaxers fall into two main categories based on their active ingredient. Lye relaxers use sodium hydroxide, while no-lye relaxers typically contain calcium hydroxide or guanidine carbonate. No-lye formulas are often marketed as a gentler option, but research tells a more complicated story.
A study measuring the pH of both types found no significant difference between them. The median pH across all relaxers tested was 12.36, which is highly alkaline and corrosive to skin regardless of the formula. Products marketed for children showed the same pH levels as those for adults. Lye relaxers tend to process faster and produce a silkier result, but they’re more likely to cause immediate scalp irritation. No-lye relaxers work more slowly and can leave calcium deposits on the hair that make it feel dry over time. Neither type is truly “gentle” in a chemical sense.
What the Application Process Looks Like
Before the relaxer cream goes on, a stylist (or the person applying at home) coats the scalp and hairline with a thick protective base, usually petroleum jelly or a wax-based cream. This barrier helps prevent chemical burns from direct contact with the highly alkaline product.
The relaxer cream is then applied to new growth only, starting at the back of the head where hair is thickest. It’s left on for a set amount of time, typically 15 to 20 minutes depending on hair texture and the product’s strength. Timing matters: leaving it on too long can dissolve the hair’s protein structure and cause severe breakage. After processing, the hair is rinsed thoroughly and a neutralizing shampoo is applied to stop the chemical reaction and bring the hair’s pH back to a normal range.
Touch-ups should only be applied to new growth at the root, not re-applied to previously relaxed hair. Overlapping the chemical onto already-processed sections is one of the most common causes of breakage.
Common Side Effects and Damage
Because relaxers are corrosive by nature, some degree of risk comes with every application. The most frequent problems are scalp irritation, burns, hair thinning, and breakage. Scratching your scalp or shampooing in the days before a relaxer can create micro-abrasions that make burns more likely.
Over time, repeated chemical processing weakens the hair shaft. Early signs of damage include increased breakage, thinning along the hairline and temples, and a rough or straw-like texture. If hair is also subjected to tight styling (ponytails, braids, weaves), the combination can lead to traction alopecia, a form of hair loss that starts with thinning at the edges and temples. In its early stages, this is reversible if the tension and chemical damage stop. If it continues, the hair follicles can scar over permanently.
The Link to Uterine Cancer
A large NIH study following 33,497 women over nearly 11 years found a connection between frequent hair straightening product use and uterine cancer. Women who used these products more than four times in the previous year were more than twice as likely to develop uterine cancer compared to non-users. The estimated lifetime risk by age 70 rose from 1.64% for non-users to 4.05% for frequent users.
The study’s lead author, Alexandra White of the National Institute of Environmental Health Sciences, noted that the doubling rate is concerning but that uterine cancer remains relatively rare overall. Notably, no similar associations were found for hair dyes, bleach, highlights, or perms. The concern centers specifically on chemical straightening products, which may contain compounds that act as endocrine disruptors and are absorbed through the scalp.
Maintaining Relaxed Hair
Relaxed hair has been chemically altered in a way that strips some of its natural protein and moisture. Keeping it healthy requires deliberate attention to both. Moisture keeps relaxed hair soft and flexible, while protein treatments rebuild strength in the weakened shaft. The goal is balance: too much moisture makes hair limp and prone to stretching until it snaps, while too much protein makes it stiff and brittle.
A practical routine involves alternating between moisturizing deep conditioners and protein-based treatments every few weeks. Light protein treatments containing keratin or hydrolyzed wheat protein can be used monthly or whenever hair starts to feel mushy or overly soft. Always follow a protein treatment with a moisturizing conditioner to restore elasticity. Between washes, water-based leave-in conditioners and creams with ingredients like glycerin or aloe vera help maintain hydration.
Touch-ups are generally recommended every 6 to 8 weeks, though some people stretch to 10 or 12 weeks without problems. Going longer between applications reduces cumulative chemical exposure but requires managing two different textures at the root line. Relaxing too frequently, anything under six weeks, risks over-processing and progressive weakening of the hair.