5.3 The pH Scale and FDA Law Governing Hair Care Products

The pH Scale and FDA Law Governing Hair Care Products

Exam Focus: This section covers two very different high-yield areas. On pH, know the logarithmic tenfold rule, the acid mantle range, and the no-water-no-pH rule. On FDA law, know that cosmetics need no pre-market approval, that the coal-tar dye exemption depends on the caution statement and patch-test direction, and that this federal rule is the reason your predisposition test is non-negotiable.

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1. The pH Scale & Acid-Base Chemistry

pH stands for potential Hydrogen (or the power of hydrogen). The pH scale measures the relative concentration of hydrogen ions ($H^+$) versus hydroxide ions ($OH^-$) in a liquid substance.

$\text{Acidic Solution: } [H^+] > [OH^-] \quad\quad \text{Alkaline Solution: } [OH^-] > [H^+]$

                                THE pH SCALE (0 - 14)

  ◄─── MORE ACIDIC ─────────────── NEUTRAL ─────────────── MORE ALKALINE ───►
 ┌───┬───┬───┬───┬───┬───┬───┬───────┬───┬───┬───┬───┬───┬───┬───┐
 │ 0 │ 1 │ 2 │ 3 │ 4 │ 5 │ 6 │   7   │ 8 │ 9 │ 10│ 11│ 12│ 13│ 14│
 └───┴───┴───┴───┴───┴───┴───┴───────┴───┴───┴───┴───┴───┴───┴───┘
   ▲           ▲       ▲         ▲         ▲           ▲       ▲
   │           │       │         │         │           │       │
 Battery   Vinegar/ Hair/Skin   Pure   Cold Waves/  Lightener Lye
  Acid      Neutral   Acid     Water    Ammonia      Bleach  Relaxer
            (Perm)   Mantle             Haircolor
                    (4.5-5.5)

The Mandatory Water Requirement for pH

Fundamental Chemistry Rule: Only aqueous (water-containing) solutions or substances that dissolve in water can possess a pH. Pure anhydrous substances—such as mineral oils, silicones, waxes, pure alcohol, and dry powder crystals—HAVE NO pH because they do not contain water and cannot ionize into $H^+$ and $OH^-$ ions.

The Logarithmic Nature of the pH Scale

The pH scale is a logarithmic scale, meaning that each whole numerical unit represents a tenfold (10×) change in ion concentration:

• A pH of 6 is 10 times more acidic than pH 7.
• A pH of 5 is 100 times ($10 \times 10$) more acidic than pH 7.
• A pH of 4 is 1,000 times ($10 \times 10 \times 10$) more acidic than pH 7.
• A pH of 3 is 10,000 times ($10 \times 10 \times 10 \times 10$) more acidic than pH 7.
• A chemical relaxer at pH 13 is 1,000,000 times more alkaline than neutral pure water (pH 7) and 100,000,000 times more alkaline than the natural hair acid mantle (pH 5)!

The Natural Acid Mantle (pH 4.5 – 5.5)

Human skin and hair are naturally coated with a micro-thin protective barrier known as the acid mantle, formed by a biological mixture of sebum (secreted by sebaceous glands), sweat (secreted by sudoriferous glands), and cellular lipids. The natural pH of healthy hair and skin ranges strictly between 4.5 and 5.5.

The acid mantle fulfills three vital biological roles:

1. Inhibits microbial growth: Prevents colonization by harmful pathogenic bacteria and fungi.
2. Preserves moisture: Prevents excessive transepidermal water loss (TEWL).
3. Maintains cuticle integrity: Keeps keratin cuticle scales tightly compressed, flat, and reflective.

Structural Effects of Acids vs. Alkalines on Hair & Skin

┌────────────────────────────────────────┬────────────────────────────────────────┐
│             ACIDS (pH < 7)             │           ALKALINES (pH > 7)           │
├────────────────────────────────────────┼────────────────────────────────────────┤
│ • Contract, harden, and tighten tissues │ • Soften, swell, and expand tissues    │
│ • Compact and close hair cuticle scales│ • Open and lift hair cuticle scales    │
│ • Restore natural acid mantle          │ • Permit penetration into hair cortex  │
│ • Add shine and reduce frizz           │ • Excessive alkalinity dissolves       │
│ • Neutralize alkaline chemical residues│   keratin protein bonds                │
└────────────────────────────────────────┴────────────────────────────────────────┘

Master Table of Salon Chemical pH Ranges

2. FDA Law Governing Hair Care Products and Product Safety

The Federal Food, Drug, and Cosmetic Act (FD&C Act) governs what may be sold as a cosmetic in the United States and what the label must say. New York's curriculum names it because a cosmetologist applies these products to other people's skin.

Cosmetic or drug?

Shampoo is a cosmetic; anti-dandruff shampoo is a cosmetic and a drug, because controlling dandruff is a therapeutic claim. Ordinary conditioner is a cosmetic; a product claiming to regrow hair is a drug. That distinction, incidentally, is also why New York exempts medicated dandruff shampoos and hair-regrowth treatments from sales tax while taxing ordinary retail hair products — they are classified as drugs.

What the FD&C Act actually requires of cosmetics

• No pre-market approval, but the product must be safe under labelled or customary conditions of use and must not be adulterated or misbranded.
• Ingredient labelling in descending order of predominance on products sold to consumers.
• Colour additives used in cosmetics generally must be approved by the FDA for the specific intended use, and many must be batch-certified.
• Prohibited and restricted ingredients — a limited list that the FDA bans or restricts outright.

The coal-tar hair dye exemption — and why your patch test exists

Oxidative permanent hair colour uses aniline derivative dyes, which the FD&C Act treats as coal-tar hair dyes. These are given a statutory exemption from the colour additive approval requirement, conditional on labelling. To qualify, the label must bear a caution statement to the effect that:

This product contains ingredients which may cause skin irritation on certain individuals and a preliminary test according to accompanying directions should first be made. This product must not be used for dyeing the eyelashes or eyebrows; to do so may cause blindness.

Two professional consequences follow, and both are heavily tested.

1. The predisposition (patch) test is a manufacturer instruction with federal backing. Because the exemption depends on directing a preliminary test, the manufacturer's directions call for a patch test 24 to 48 hours before each application of aniline derivative colour. Chapter 11 covers the procedure. A client who has tolerated the colour for years can still develop sensitisation, which is why the test is repeated rather than performed once.
2. Eyelash and eyebrow dyeing with these products is prohibited. The caution statement is explicit, and 19 NYCRR § 160.27(e) independently bars a New York appearance enhancement licensee from applying dye of any kind to eyelash or eyebrow hair — with one narrow exception. Products containing silver nitrate colour additives authorised by the FDA under 21 CFR § 73.2550 may be used to tint lash or brow hair, applied exactly as the manufacturer directs. Nothing else is permitted, whatever the product is marketed as.

Product safety habits that follow from the law

• Keep the original label intact — required by 19 NYCRR § 160.26 and the only place the caution statement and directions live.
• Follow the manufacturer's directions, which § 160.17(a)(1) makes binding for disinfectants and which the FD&C Act makes the condition of the coal-tar exemption for dyes.
• Read the ingredient list when a client reports a reaction, and record what was used, at what volume, for how long, on the client record card.
• Do not rely on marketing terms. "Natural", "organic", "hypoallergenic" and "chemical-free" have no fixed regulatory meaning for cosmetics, and none of them removes the need for a patch test.
• Report serious reactions. A serious adverse event should be reported to the manufacturer and may be reported to the FDA; the client should be referred to a physician.