4.2 Matter, the pH Scale & Product Chemistry

Every color, relaxer, perm, shampoo, and EPA disinfectant you touch is matter in a particular physical state—solid powder lightener, liquid developer, gas (the fumes ventilation is supposed to remove). Chemistry questions on the theory exam rarely ask you to balance equations. They ask whether you can tell a physical change (the same substance, different form—ice melting, a suspension that settles) from a chemical change (a new substance forms—melanin oxidized by bleach, disulfide bonds broken by a thio wave). They also ask whether you can read pH well enough to know why a hydroxide relaxer is a different animal from an acid-balanced wave.

Building blocks: elements, compounds, and mixtures

An atom is the smallest unit of an element (oxygen, hydrogen, sodium). A molecule is two or more atoms bonded; a compound is a molecule made of different elements in a fixed ratio (water is H2O; hydrogen peroxide is H2O2). Salon products are almost never a single compound. They are mixtures. How that mixture behaves on the shelf and on the hair is the exam skill.

Emulsions split by which liquid is the outer, continuous phase. Oil-in-water (O/W) emulsions have tiny oil droplets in water. They usually feel lighter, rinse with water, and make up most leave-in lotions and many cream products. Water-in-oil (W/O) emulsions have water droplets in oil. They feel heavier, resist water, and show up as richer creams (think classic cold-cream texture). If a question describes a product that rinses easily and uses water as the outer phase, you want oil-in-water.

A surfactant (surface-active agent) is the molecule that makes emulsions and shampoos work. It has a hydrophilic (water-loving) head and a lipophilic (oil-loving) tail. The tails bury themselves in sebum and oil; the heads stay in water, so dirt can be emulsified and rinsed. Shampoo surfactants are often anionic (good cleansing). Conditioners often use cationic surfactants that are attracted to negatively charged hair. Nonionic surfactants are milder. Amphoteric surfactants change behavior with pH. You do not need to memorize brand trade names; you need the hydrophilic/lipophilic picture and the idea that the same architecture that cleans hair also holds a cream together.

The pH scale is logarithmic, not a popularity contest

pH (“potential of hydrogen”) measures the concentration of hydrogen ions in a water-based product. The scale runs 0 to 14. 7 is neutral (pure water). Below 7 is acidic (more H+). Above 7 is alkaline (also called basic; more OH−). The scale is logarithmic: each whole-number step is a tenfold change. A hydroxide relaxer near pH 13 is not “a little more alkaline” than a thio product near pH 10; it is about 1,000 times more alkaline (10 × 10 × 10). That is why hydroxide services demand a different respect than a daily shampoo.

Hair and skin are not pH 7. The acid mantle—the thin acidic film of sebum, sweat, and natural moisturizing factors—typically sits near pH 4.5–5.5. That acidity helps the cuticle lie flatter, keeps moisture in, and is part of the skin’s barrier. Products well above the acid mantle swell the cortex and lift the cuticle. Products at or below the acid mantle contract the cuticle and often make hair feel smoother. That single mechanical fact explains half of product chemistry.

Where salon products sit on the scale

Exact pH is always the number on that bottle’s SDS or technical sheet. Theory items use typical ranges, not a secret Oklahoma Board pH chart—the Board does not publish one. Use these working ranges as a map, then still read the label:

• Strong acids (far below 7): some rust removers and acid-type cleaners you should never dump into a sodium hypochlorite wet sanitizer; a few specialty acid rinses.
• Conditioners and many acid rinses: commonly about 3.5–5.5, designed to close the cuticle after shampooing or chemical work.
• Hair and skin acid mantle: about 4.5–5.5.
• Many modern daily shampoos: often near 5–7. Classic teaching still treats a more alkaline shampoo as a stronger cleanser that opens the cuticle more; a clarifying shampoo is commonly more alkaline than a daily shampoo so it can strip mineral and product buildup.
• Hydrogen peroxide in developer is typically acidic in the bottle (often around pH 3–4) so it stays more stable; the color or lightener formula you mix it into is what drives the working pH up.
• Acid waves (glyceryl monothioglycolate, GMTG): true acid waves are often taught near pH 4.5–7.0 and usually need heat; acid-balanced waves commonly sit about pH 7.8–8.2, still milder swelling than a cold wave.
• Alkaline / cold waves (ammonium thioglycolate, ATG): typically about pH 9.0–9.6, process without added heat, more cuticle lift, faster processing on resistant hair.
• Thio relaxers (ammonium thioglycolate family): typically about pH 9–10, alkaline enough to soften disulfide bonds but not in the hydroxide stratosphere.
• Hydroxide relaxers (sodium, lithium, potassium, or guanidine hydroxide): typically about pH 12–14. They perform lanthionization—disulfide bonds are converted to lanthionine and cannot be rebuilt the way a thio wave’s bonds can be oxidized back. That is a chemistry difference, not a marketing slogan.

Alkaline chemical services are not “bad pH.” They are tools. You choose them because you want the cuticle open so waving lotion, relaxer, or color can reach the cortex. You then use an acidic or acid-balanced follow-up—conditioner, neutralizing shampoo after a hydroxide relaxer, or an oxidizing neutralizer after a thio wave or perm—to bring the fiber back toward the acid mantle. Skipping that return trip leaves the cuticle rough, tangled, and chemically thirsty.

Hydrogen peroxide as the workhorse oxidizer

Hydrogen peroxide (H2O2) is an oxidizing agent: it donates oxygen and accepts electrons. In haircolor, mixed as the manufacturer directs, it develops dye intermediates into larger color molecules and can lighten natural melanin. In lightener, persulfate boosters plus peroxide oxidize melanin more aggressively. In thio perm and thio relaxer neutralizing, peroxide (or sometimes sodium bromate, depending on the labeled system) rebuilds disulfide bonds by oxidation. Volume is concentration: 10 volume ≈ 3%, 20 volume ≈ 6%, 30 volume ≈ 9%, 40 volume ≈ 12%. Higher volume is not a personality trait; it is more available oxygen and more lift—and more potential for scalp irritation if used off-label.

Keep peroxide in its original dark container as the label requires; heat, light, and metal contamination speed decomposition (you will see extra bubbling). OAC 175:10-7-3 still applies: do not pour developer into a food bottle, and do not invent a mix the color label does not print. Peroxide plus ammonia inside a labeled haircolor formula is an intended manufacturer mixture. Peroxide chemistry is not the same thing as mixing sodium hypochlorite disinfectant bleach with ammonia—that trap belongs to the next section.

When a scenario says “the hair feels rough and the cuticle is raised after shampooing,” think alkaline cleansing without an acid closer. When it says “the relaxer is a no-lye guanidine hydroxide,” still think pH 12–14 chemistry, not a gentle conditioner. “No-lye” means it is not sodium hydroxide; it does not mean it is near the acid mantle. That vocabulary trap shows up because clients hear “no-lye” as “no chemistry.” You should not.