13.3 pH, Water, and Cosmetic Chemistry
Key Takeaways
- pH runs from 0 to 14; 7 is neutral; each whole-number step is a tenfold change in hydrogen-ion concentration; hair and skin acid mantle is about 4.5 to 5.5; typical shampoo sits about 4.5 to 7.
- Lye versus no-lye relaxer chemistry is hair design, not Oregon barbering — a trap if an item asks a barber to choose sodium hydroxide for a service.
- Water is the universal solvent; hard water is high in calcium and magnesium; distilled water has been boiled and condensed; purified water has minerals and ions removed by filtration or deionization.
- At exam depth: elements cannot be broken down chemically; compounds are elements chemically combined (water is H2O); mixtures are physically combined. Solutions stay mixed; suspensions settle; emulsions are oil-in-water or water-in-oil.
- Oxidation in a hair lightener is out of barbering scope. Oregon barbers do not bleach. Treat a lightener-oxidation item as a trap.
Chemistry is 4 of 100 Barbering Examination items: pH and the pH scale, water, and cosmetic chemistry. That is the last slice of the 11-item Product Knowledge and Chemistry block. HLO still draws the science from Milady 5th edition and Pivot Point. Oregon then filters it through scope. Lye versus no-lye relaxers are hair design, not barbering. Oxidation in a lightener is the same trap. Learn the scale, the solvent, and the mixture types so you can answer the four items without wandering into a color class you are not licensed to give.
pH (potential hydrogen) measures how acidic or alkaline a water-based solution is. The scale runs 0 to 14. 7 is neutral — equal hydrogen ions (H+) and hydroxide ions (OH−). Below 7 is acid. Above 7 is alkaline (also called base). Each whole-number step is a tenfold change: pH 5 is ten times more acidic than pH 6, and one hundred times more acidic than pH 7. Pure water is taught as pH 7. Hair and the acid mantle of skin sit on the acid side, commonly about 4.5 to 5.5. That slightly acid film helps the cuticle lie flatter and helps skin resist some microbes. It is not a medical barrier you "prescribe." It is why you do not park daily shampoo at pH 12.
Acid solutions tend to contract and harden the cuticle (close it). Alkaline solutions tend to swell and soften the cuticle (open it). That is why a pH-balanced shampoo in the 4.5 to 7 window cleans without aggressively lifting the scales, and why an alkaline clarifying shampoo above 7 strips more oil and leftover wax. Conditioners are usually acid so they help the cuticle lie down after the wash.
The pH scale you must be able to read
| pH | Acid or alkali | Relative to neutral (pH 7) | Barber-relevant example |
|---|---|---|---|
| 0–1 | Strong acid | Millions of times more H+ | Battery acid — not a shop product |
| 2–3 | Acid | Tens to hundreds of thousands times | Some fruit acids; not a relaxer |
| 4.5–5.5 | Acid | Hair and skin acid mantle | Intact cuticle and skin surface |
| 4.5–7 | Slightly acid to neutral | Typical shampoo range | pH-balanced daily shampoo |
| 7 | Neutral | Equal H+ and OH− | Pure water |
| 8–9 | Alkaline | Cuticle opens | Soap; some clarifying shampoos |
| 10–11 | Alkaline | Stronger swell | Some soaps and cleaners |
| 12–14 | Strong alkali | Lye range | Sodium hydroxide relaxer — hair design, not barbering |
Memorize the three shop numbers: acid mantle 4.5 to 5.5, shampoo typically 4.5 to 7, neutral 7. Then remember that lye (sodium hydroxide) lives at the far alkaline end and is not an Oregon barbering service. No-lye relaxers (guanidine hydroxide, lithium hydroxide, and similar textbook names) are still relaxers. They still restructure hair. They still belong to hair design under ORS 690.005. The item that asks a barber which relaxer is "safer for the scalp" is a scope trap, not a product-choice item.
Water as the universal solvent
Water is the universal solvent in cosmetic chemistry: more substances dissolve in water than in any other common liquid. Almost every shampoo, conditioner, and water-based gel is a water solution or a water emulsion. That is also why pH is defined on water-based products. Anhydrous (waterless) oils do not have a meaningful pH in the same way.
| Water type | What it is | Shop consequence |
|---|---|---|
| Hard water | High in calcium and magnesium | Poor lather; mineral film; soap scum with true soap |
| Soft water | Low mineral content | Easy lather; can over-cleanse with a strong detergent |
| Distilled water | Boiled and condensed; minerals left behind | Used when a formula must not carry tap minerals |
| Purified water | Minerals and ions removed by filtration, reverse osmosis, or deionization | Lab-clean water for mixing; not a restroom-sink substitute |
Oregon facility water is still hot and cold running water on the premises, not a restroom sink (OAR 817-010-0014). Distilled water in a jug does not replace that plumbing rule. Distilled and purified water matter on the chemistry items as definitions. Hard versus soft water matter at the bowl as lather and film.
Cosmetic chemistry: solutions, suspensions, emulsions, ointments, powders
At exam depth, sort matter first, then sort mixtures.
- An element cannot be broken down by ordinary chemical means (oxygen, carbon, hydrogen).
- A compound is two or more elements chemically combined in definite proportion. Water is the compound H2O, not a mixture of hydrogen gas and oxygen gas sitting in a glass.
- A mixture is two or more substances physically combined. They can be separated without breaking chemical bonds. Almost every shop product is a mixture.
Then sort the mixtures you actually pour:
| Form | What it is | How you know | Shop example |
|---|---|---|---|
| Solution | Solute dissolved in solvent; stable | Does not separate on standing; usually transparent or uniformly mixed | Salt water; some liquid tonics |
| Suspension | Undissolved particles in a fluid | Separates; must be shaken | Some liquid powders and calamine-type lotions |
| Emulsion | Two immiscible liquids held by an emulsifier (often a surfactant) | Creamy; may be O/W or W/O | Most cream conditioners, many creams |
| Oil-in-water (O/W) | Oil droplets in water | Usually lighter; often rinses | Most shampoos and rinse-out creams |
| Water-in-oil (W/O) | Water droplets in oil | Heavier, greasier feel | Some cold creams and heavy pomade-type creams |
| Ointment | Semisolid, often a petrolatum or similar base | Does not flow like a lotion | Some protective dressings |
| Powder | Solid particles | Dry until mixed or applied | Dry shampoo; styptic powder |
O/W versus W/O is the emulsion fork the bulletin is aiming at. If water is the outer phase, the product usually feels lighter and rinses. If oil is the outer phase, the product feels heavier and resists water. A surfactant or other emulsifier keeps the droplets from immediately separating. When an emulsion "breaks," it has failed as a mixture — oil and water show as layers — and you do not put that product on a client.
Oxidation in a lightener is a trap
Hair lightener (bleach) oxidizes melanin so the hair appears lighter. That redox story is standard in a hair-design or cosmetology color class. It is out of Oregon barbering scope. Do not spend exam minutes balancing a developer volume or naming a decolorization stage. If an item asks you to apply a lightener, pick the answer that the service is hair design, not barbering. Shampoo chemistry can involve mild oxidation in some specialty formulas, but the bulletin's chemistry items are pH, water, and mixture types — not a license to bleach.
OAR 817-005-0005 still calls a product that restructures or removes hair a chemical service. Removal of hair with a razor is a shave. Removal of color with bleach is not a shave. Keep those sentences separate when a stem uses the word "chemical."
A Salem candidate and a lye item
A walk-in candidate at HLO, 1430 Tandem Ave. NE, Suite 180, Salem, sees an item that names sodium hydroxide, no-lye guanidine, and a pH 4.5 shampoo, and asks which product an Oregon barber uses to permanently straighten coarse hair. The shampoo is in scope and is the wrong service. Both relaxers restructure hair and are hair design. The correct barber move is not to pick the "milder" relaxer. It is to recognize that lye versus no-lye is not barbering. The same candidate should still be able to mark acid mantle 4.5 to 5.5, neutral 7, hard water as calcium and magnesium, and O/W versus W/O. Those are the four chemistry items. The lightener-oxidation story is how a fifth, out-of-scope idea steals the clock.
On the pH scale used in barbering theory, where do hair and the acid mantle of skin commonly sit, and where does a typical shampoo sit?
An Oregon Barbering Examination item describes oxidation of melanin by a hair lightener. What is the correct barbering response?
Which statement matches exam-depth water and mixture chemistry for Oregon barbering?