Chemical Services (Color, Perms, Relaxers)
Color, perms, and relaxers permanently change the hair through chemistry, so they carry both the greatest creative power and the greatest risk. This chapter covers the pH scale as it applies to hair, how oxidative haircolor works, the contrasting chemistry of thio perms and hydroxide relaxers, and the essential safety tests you must perform first.
pH and the Hair
The pH scale runs 0 to 14, with 7 neutral. Below 7 is acidic; above 7 is alkaline. Alkaline products swell the hair and raise the cuticle, which is why permanent colors, lighteners, and cold-wave perms are alkaline — they need the cuticle open to reach the cortex. Acidic products contract and smooth the cuticle, which is why many conditioners and toners are slightly acidic. The scale is logarithmic, so each whole number is a tenfold change; small differences in pH have large real effects on the hair.
Oxidative Haircolor and Lighteners
Permanent haircolor works by oxidation. An alkaline agent (usually ammonia) swells the cuticle, while hydrogen peroxide (the developer) releases oxygen that lifts natural melanin and causes small dye precursors to join into larger colored molecules trapped in the cortex. Higher developer volume means more lift (for example, 20 volume lifts more than 10 volume). Lighteners (bleach) use peroxide, often boosted, to diffuse melanin. Because these are permanent chemical changes, correct formulation and timing are essential.
Perms vs. Relaxers, and Required Tests
Ammonium thioglycolate ('thio') perms break the hair's disulfide bonds by reduction; the hair is molded on rods, then an oxidizing neutralizer rebuilds the bonds in the new curl. Hydroxide relaxers (sodium/'lye', or 'no-lye' guanidine) straighten by a different, non-reversible reaction (lanthionization) and are stopped by thorough rinsing plus an acid-balanced neutralizing shampoo — not by an oxidizing neutralizer. Thio and hydroxide chemistries are not compatible on the same hair. Always perform the right pre-service tests: a patch (predisposition) test 24-48 hours before aniline-derivative color to check for allergy, and a strand test to preview the result and check the hair's strength and porosity.