4.1 Chemistry Fundamentals, pH Scale & Chemical Bonds

Chemistry Fundamentals: Organic vs. Inorganic Chemistry & Matter

Chemistry is the scientific discipline that studies the composition, structures, properties, and transformations of matter. Every professional service performed in the modern salon—from permanent waving and chemical hair relaxing to oxidative hair coloring and skin exfoliation—is governed by chemical principles. A licensed cosmetologist must possess a thorough understanding of foundational chemistry to safely formulate, apply, and neutralize salon chemicals without compromising client safety or hair structural integrity.

1. Organic vs. Inorganic Chemistry

For licensing examinations, chemistry is divided into two primary branches based entirely on the presence of the element carbon:

• Organic Chemistry: The branch of chemistry dealing with substances that contain the element carbon (C). Organic matter originates from living or once-living organisms (plants and animals) or synthetic carbon-based polymers. Crucially, most organic substances are flammable and will burn. Examples in cosmetology include natural hair, skin, nails, synthetic hair extensions, petroleum jelly, styling polymers, shampoos, conditioners, and oxidative hair color molecules.
• Inorganic Chemistry: The branch of chemistry dealing with substances that do not contain carbon (with a few minor exceptions such as carbon monoxide and carbon dioxide). Inorganic substances are non-living minerals that were never alive and generally will not burn. Examples in cosmetology include pure distilled water (H2O), hydrogen peroxide (H2O2), salon minerals, titanium dioxide in sunscreen, elemental metals (shears, implements), and atmospheric oxygen (O2).

State Board Exam Tip: Do not confuse the everyday marketing definition of "organic" (meaning pesticide-free or natural) with the chemical definition. In cosmetology chemistry, motor oil, gasoline, synthetic plastics, and chemical relaxers are strictly classified as organic substances because their molecular structures contain carbon atoms.

2. Matter and Its States

Matter is defined as anything that occupies physical space and has mass (weight). All matter in the universe exists in one of three physical states depending on temperature and atmospheric pressure:

1. Solids: Possess a definite shape and definite volume. The molecules are tightly packed in fixed arrangements with minimal kinetic energy (e.g., styling combs, ice, ice packs, solid soap bars, acrylic nail enhancements).
2. Liquids: Possess a definite volume but an indefinite shape, adopting the shape of their container. Molecules are loosely packed and flow freely past one another (e.g., shampoos, liquid developers, waving lotions, water).
3. Gases: Possess neither a definite shape nor a definite volume. Gas molecules are widely dispersed and expand indefinitely to fill any container (e.g., propellant gases in aerosol hairsprays, ammonia gas vapor released during hair coloring, atmospheric air).

3. Physical vs. Chemical Properties and Changes

Cosmetologists manipulate physical and chemical properties constantly during salon services:

• Physical Properties: Characteristics that can be observed or measured without altering the chemical identity or composition of the substance. These include color, odor, density, melting point, boiling point, hardness, and solubility.
• Chemical Properties: Characteristics that can only be determined by a chemical reaction and a resulting chemical change in the substance. Examples include the ability of iron to rust, the ability of hair color to oxidize, and the flammability of aerosol hairsprays.
• Physical Change: A transformation in which the physical form or physical appearance of a substance is altered without creating a new chemical substance. No chemical bonds are broken or created. Examples include:
  • Water freezing into solid ice or evaporating into steam.
  • Cutting, trimming, or filing the hair and nails.
  • Temporary thermal styling (flat ironing or curling hair), which temporarily disrupts physical hydrogen bonds.
  • Dissolving sugar or salt into water.
• Chemical Change: A transformation that produces entirely new chemical substances with distinct chemical and physical properties through chemical reactions. Chemical changes involve the rearrangement of molecular bonds. Examples include:
  • Oxidative Hair Coloring: Developer (H2O2) oxidizes melanin granules and couples color precursor molecules inside the cortex.
  • Permanent Waving: Alkaline or acid waving lotions reduce and break cystine disulfide bonds, which are subsequently rebuilt by an oxidizing neutralizer.
  • Chemical Hair Relaxing: Hydroxide relaxers chemically break disulfide bonds and convert them into permanent lanthionine bonds (lanthionization).

Oxidation-Reduction (Redox) Reactions & Hair Bond Chemistry

1. Oxidation-Reduction (Redox) Dynamics

A substantial portion of salon chemical services relies on Oxidation-Reduction (Redox) reactions. An oxidation-reduction reaction is a paired chemical reaction in which oxidation and reduction occur simultaneously:

• Oxidation: A chemical reaction that involves the addition of oxygen, the loss of hydrogen, or the loss of electrons. The substance that gains oxygen or loses electrons is oxidized.
• Reduction: A chemical reaction that involves the loss of oxygen, the addition of hydrogen, or the gain of electrons. The substance that loses oxygen or gains electrons is reduced.

Oxidizing agent (gains electrons / loses O2) + Reducing agent (loses electrons / gains O2) -> Redox reaction

Key Salon Reagents in Redox Reactions

1. Oxidizing Agent: A substance that releases oxygen or absorbs electrons. The most ubiquitous oxidizing agent in cosmetology is Hydrogen Peroxide (H2O2), used as the developer / catalyst in permanent hair coloring, hair lighteners, and permanent wave neutralizers.
2. Reducing Agent: A substance that subtracts oxygen from a compound or donates hydrogen/electrons. The primary reducing agent in salon chemical waving and curling is Thioglycolic Acid (or Ammonium Thioglycolate), which donates hydrogen atoms to break the hair's internal disulfide cross-links.

+-------------------------------------------------------------------------+
|                    REDOX REACTION IN PERM PROCESSING                    |
|                                                                         |
|  1. REDUCTION PHASE (Perm Lotion / Reducing Agent):                     |
|     Keratin-S-S-Keratin  +  2[H] (from Thioglycolate)                   |
|     --> Keratin-S-H  +  H-S-Keratin  (Disulfide Bonds Broken)           |
|                                                                         |
|  2. OXIDATION PHASE (Neutralizer / Oxidizing Agent):                    |
|     Keratin-S-H  +  H-S-Keratin  +  [O] (from H2O2)                     |
|     --> Keratin-S-S-Keratin  +  H2O  (Disulfide Bonds Rebuilt)          |
+-------------------------------------------------------------------------+

2. The Structural Cross-Bonds of Hair Keratin

The hair shaft is composed of fibrous polypeptide protein chains coiled into a helical structure called alpha-keratin. These protein chains are held together side-by-side by three distinct types of cross-bonds that account for the hair's tensile strength, elasticity, and shape:

• Hydrogen Bonds: Weak, physical, cross-linked side bonds formed between adjacent positive and negative charges. They are easily broken by water or thermal heat and are reformed as the hair dries or cools. Although individually weak, hydrogen bonds exist in such massive quantities that they account for approximately one-third (33%) of the hair's total structural strength.
• Salt Bonds: Weak, physical, ionic cross-linked side bonds formed between the positive amino acid groups and negative carboxyl groups of adjacent polypeptide chains. Salt bonds are easily broken by changes in pH (strong acidic or alkaline solutions) and reform when the pH of the hair is restored to its normal acidic range (pH 4.5–5.5). They also account for one-third (33%) of the hair's lateral strength.
• Disulfide Bonds: Strong, covalent chemical side bonds formed when the sulfur atoms of two adjacent cysteine amino acids link together to create cystine. Disulfide bonds are not broken by water, heat, or ordinary stretching. They can only be broken by chemical reducing agents (such as thioglycolate lotions), hydroxide chemical relaxers, or extreme thermal destruction. Disulfide bonds represent the remaining one-third (33%) of the hair's total strength and determine the permanent curl pattern.

The pH Scale: Potential Hydrogen, Ion Concentrations & Salon Reference Standards

1. Understanding Potential Hydrogen (pH)

The term pH stands for Potential Hydrogen (or power of hydrogen). The pH scale measures the relative concentration of Hydrogen ions (H+) versus Hydroxide ions (OH-) in an aqueous (water-based) solution.

• Water Dependency: A substance must contain water or be dissolvable in water to have a measurable pH. Pure oils, alcohol, anhydrous styling waxes, and mineral powders have no pH because they contain no water and do not dissociate into hydrogen or hydroxide ions.
• Ion Balance: Pure distilled water dissociates into equal numbers of hydrogen (H+) and hydroxide (OH-) ions, creating a completely neutral state (pH 7.0):

H2O <=> H+ + OH- (equal concentrations at pH 7.0)

• Acids (pH 0.0 to 6.9): Solutions that contain a higher concentration of Hydrogen ions (H+) than hydroxide ions. Acids taste sour, turn blue litmus paper red, contract and harden the hair protein, and tighten the cuticle layer.
• Alkalis / Bases (pH 7.1 to 14.0): Solutions that contain a higher concentration of Hydroxide ions (OH-) than hydrogen ions. Alkalis feel slippery, turn red litmus paper blue, soften and swell the hair structure, and open the protective cuticle scales.

2. The Logarithmic Nature of the pH Scale

The pH scale is logarithmic, not linear. This means that each whole number jump on the scale represents a tenfold (10x) change in the concentration of hydrogen or hydroxide ions:

• A pH of 8 is 10 times more alkaline than pure neutral water (pH 7).
• A pH of 9 is 100 times (10 x 10) more alkaline than pure neutral water (pH 7).
• A pH of 10 is 1,000 times (10 x 10 x 10) more alkaline than pure neutral water (pH 7).
• A pH of 13 (typical hydroxide relaxer) is 1,000,000 times (10 to the 6th power) more alkaline than pure neutral water (pH 7) and 100,000,000 times (10 to the 8th power) more alkaline than natural hair (pH 5).

State Board Calculation Tip: To calculate the difference between two pH values, subtract the smaller number from the larger number to find the exponent of 10. For example, comparing pH 5 (skin) to pH 9 (hair color): 9 - 5 = 4 zeros, meaning pH 9 is 10 to the 4th power, or 10,000 times more alkaline than skin.

+-----------------------------------------------------------------------------+
|                             THE LOGARITHMIC pH SCALE                        |
|                                                                             |
|   ACIDIC (Excess H+ Ions)        NEUTRAL        ALKALINE (Excess OH- Ions)  |
|  [Cuticle Closes & Hardens]     [H+ = OH-]     [Cuticle Swells & Opens]     |
|                                                                             |
|   0   1   2   3   4   5   6        7        8   9  10  11  12  13  14       |
|  <------------------------|--------*--------|------------------------->     |
|                           |                 |                               |
|                     Hair/Skin/Mantle    Perm / Color / Relaxers             |
|                       (pH 4.5–5.5)          (pH 8.0–14.0)                   |
+-----------------------------------------------------------------------------+

3. The Acid Mantle and Cuticle Dynamics

The surface of human skin, scalp, and the cuticular layer of hair is naturally bathed in a delicate protective barrier called the Acid Mantle. The acid mantle is a complex fluid mixture secreted by the sebaceous (oil) glands and sudoriferous (sweat) glands, maintaining an optimal acidic pH between 4.5 and 5.5.

• Biological Function: The acidic environment of the acid mantle inhibits bacterial, fungal, and microbial proliferation on the scalp while preserving the compact, shingle-like arrangement of the protective hair cuticle scales.
• Chemical Action of Salon Alkalis: When alkaline chemical solutions (e.g., permanent hair color, decolorizer, or permanent wave lotion) are applied, they neutralize the acid mantle, soften the keratin, and cause the imbrications (scales) of the cuticle to lift and flare open. This allows active chemical agents to penetrate deeply into the cortex.
• Chemical Action of Salon Acids: Following an alkaline chemical service, acidic formulations (such as neutralizing shampoos, acid-balanced rinses, or post-color sealers with pH 3.0–5.0) are applied to normalize the hair's pH, contract the protein matrix, shrink the hair diameter, and lock the cuticle scales flush against the cortex.

4. Comprehensive Salon Chemical pH Reference Table

Memorizing the specific pH ranges of common salon products is vital for both the Pennsylvania licensing examination and daily clinical practice: