Chemical Relaxers: Types, Safety, and Application
Objective. Students will differentiate between hydroxide and thio relaxers by chemistry and application protocol, and safely perform a virgin hydroxide relaxer service on a mannequin including base application, processing, smooth-down, and neutralizing shampoo sequence.
This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.
VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.
Chemical Relaxers: Types, Safety, and Application
Chemical relaxers permanently straighten curly or coily hair by breaking the disulfide bonds or the peptide bonds that give each strand its natural curl pattern. Because the chemistry involved is aggressive, understanding what each relaxer type does—and how to control it—is the foundation of safe, professional service.
Two Major Relaxer Families
Hydroxide relaxers are the most widely used category in professional salons. Their active ingredient is a metal hydroxide—either sodium hydroxide (lye), potassium hydroxide, lithium hydroxide, or guanidine hydroxide (no-lye formulas). All hydroxide relaxers work at a very high pH, typically in the range of 12 to 14. At that pH, the relaxer swells the hair shaft, breaks disulfide bonds irreversibly, and converts them to lanthionine bonds—a change that cannot be reversed or rebuilt. This is the key incompatibility fact: once hair has been processed with a hydroxide relaxer, it must never receive a thio relaxer or a thio-based permanent wave. Mixing the two chemistries on the same hair causes severe damage and breakage.
- Lye relaxers contain sodium hydroxide. They process quickly, tend to leave hair smooth and shiny, and require careful application because they can irritate the scalp rapidly.
- No-lye relaxers use a two-part system—guanidine carbonate mixed with calcium hydroxide—or lithium hydroxide. They are somewhat gentler on the scalp but can leave calcium deposits on the hair over time, making regular deep conditioning essential.
Thio relaxers (thioglycolate relaxers) share their active ingredient with cold-wave permanent solutions: ammonium thioglycolate or a related mercaptan compound. Their pH is lower than hydroxide relaxers, generally in the range of 9 to 9.5. Thio relaxers break disulfide bonds temporarily and require an oxidizing neutralizer (hydrogen peroxide or sodium bromate) to reform them in a straightened position—the same basic mechanism as a permanent wave. Because the bonds are reformed rather than converted, hair that has had a thio relaxer can be re-permed with another thio product if timing and condition allow, but it absolutely cannot receive a hydroxide relaxer afterward without extreme breakage risk.
Base vs. No-Base Application
Hydroxide relaxers are classified by how much scalp protection they require before application.
- Base relaxers are formulated with enough strength to require a protective base cream applied to the entire scalp, hairline, ears, and nape before any relaxer touches the skin. Skipping this step risks chemical burns.
- No-base relaxers are slightly milder formulations designed so that base cream is applied only to the perimeter (hairline, ears, nape) rather than the full scalp. Even so, most manufacturers and instructors recommend applying base cream to any sensitive or previously irritated areas. In this lab you will use a no-base formulation, which still requires full perimeter protection.
Safety First
Chemical relaxers can cause serious chemical burns if misused. Follow every precaution below without exception.
1. Read the SDS (Safety Data Sheet) for the specific product before the lab. Know the first-aid steps for skin and eye contact.
2. Never apply relaxer to a scratched, sunburned, or irritated scalp. On real clients, postpone the service.
3. Wear gloves at all times from mixing through rinse-out. Never allow relaxer to contact your skin.
4. Do not pre-shampoo before a relaxer service. Shampooing removes the scalp's natural oil barrier and increases burn risk. On real clients, dry-section the hair only.
5. Avoid base cream on the hair shaft itself near the scalp; it can create a barrier that prevents complete relaxer penetration.
6. Never exceed the manufacturer's recommended processing time. Overprocessing causes irreversible breakage.
7. Rinse thoroughly with warm (not hot) water before shampooing. Incomplete rinsing leaves active relaxer on the scalp.
Application Protocol: Virgin Hydroxide Relaxer (Four-Section Method)
A virgin relaxer application is the first-time service on hair that has never been chemically relaxed. All hair from scalp to ends receives relaxer, with the most resistant area (usually the nape and crown) done first.
1. Preparation – Apply base cream to the full perimeter (hairline, ears, nape). On a mannequin, apply to the simulated scalp surface as directed by your instructor.
2. Section – Divide the hair into four quadrants using the four-section method: center-front to nape, and ear to ear across the crown. Clip each quadrant.
3. Application order – Begin at the most resistant section. Apply relaxer with an applicator brush approximately one-quarter inch from the scalp, working toward the ends. Apply to the scalp area last to limit heat exposure from the scalp.
4. Smooth-down – After all sections are coated, use the back of the brush or gloved fingers to smooth hair in the direction of growth. Do not overwork or stretch the hair aggressively; this increases breakage risk.
5. Set the timer – Process according to the manufacturer's directions. Perform a strand test partway through if recommended.
6. Rinse – Rinse with a steady, warm water stream for the manufacturer's recommended time—commonly five or more minutes—until the water runs completely clear.
7. Neutralizing shampoo sequence – Apply neutralizing shampoo, work into a lather, allow to sit briefly, then rinse. Repeat for a total of five passes. Neutralizing shampoo typically contains an acid-balanced pH indicator that changes color when all hydroxide residue is removed.
8. Condition – Apply a moisturizing conditioner to restore moisture and close the cuticle. Process and rinse per the manufacturer's instructions.
Why Five Shampoo Passes Matter
Hydroxide is not neutralized by an oxidizer the way thio is. The neutralizing shampoo works by mechanically removing hydroxide residue and restoring the hair's acid mantle through repeated flushing with an acidic or pH-balanced formula. Skipping passes leaves a high-pH environment on the scalp and hair shaft, which continues to degrade protein bonds even after the client leaves the salon—causing delayed breakage. The five-pass requirement in this lab is grounded in manufacturer and industry guidance and is a non-negotiable pass/fail point on your checklist.
Key terms9
Materials: Professional hydroxide relaxer (no-lye formulation for mannequin use), protective base cream, applicator brush, gloves, processing cape, timer, neutralizing shampoo, moisturizing conditioner, four-section clips, mannequin heads, SDS for relaxer product, comparison chart handout
Check: Pass/fail checklist: student must apply base cream to the full perimeter before relaxer contact, complete all five neutralizing shampoo passes with correct timing, and leave no relaxer residue on the mannequin scalp surface.
Practice check8
Answer each question, then check it. Nothing is recorded; this is your own practice.
