Chemistry for Cosmetology

Chemistry is fundamental to understanding how cosmetology products work. The pH scale, oxidation reactions, and chemical bonding are essential concepts for safe and effective salon services.

The pH Scale

pH (potential hydrogen) measures how acidic or alkaline a substance is. Understanding pH is critical because it determines how products affect hair and skin.

pH Scale Overview

Natural pH Levels

pH of Common Salon Products

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Acids vs. Alkalis in Products

Acidic Products (pH below 7)

Effects on Hair:

• Close and compact the cuticle layer
• Harden the hair shaft
• Add shine and smooth texture
• Lock in color after chemical services

Common Acidic Products:

• Conditioners
• Finishing rinses
• Color sealers
• Acid perms

Alkaline Products (pH above 7)

Effects on Hair:

• Open and lift the cuticle
• Soften and swell the hair shaft
• Allow penetration of chemicals
• Enable color deposit or bond breaking

Common Alkaline Products:

• Permanent hair color
• Lighteners (bleach)
• Alkaline perms
• Relaxers
• Clarifying shampoos

The Cuticle Response

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Chemistry of Hair Color

Oxidation in Hair Coloring

Hair color chemistry relies on oxidation - a chemical reaction that occurs when developer (hydrogen peroxide) mixes with color.

How Permanent Hair Color Works

1. Alkaline color opens the cuticle (allows penetration)
2. Developer breaks down natural melanin (lightening)
3. Oxidation develops artificial pigment (new color)
4. Color molecules enlarge inside cortex (permanent deposit)

Developer (Hydrogen Peroxide) Volumes

Color Types

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Chemistry of Permanent Waves

How Perms Work

Permanent waves restructure the hair's internal bonds to create curl patterns.

The Chemical Process

1. Waving lotion (reducing agent) breaks disulfide bonds
2. Hair is wrapped around rods in new shape
3. Bonds reform in new curl pattern
4. Neutralizer (oxidizing agent) re-hardens and locks bonds

Types of Permanent Waves

Key Chemistry Terms

• Reducing Agent: Breaks disulfide bonds (waving lotion)
• Oxidizing Agent: Reforms and hardens bonds (neutralizer)
• Disulfide Bonds: Strong bonds giving hair its shape
• Processing Time: Time needed for chemical action

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Chemistry of Relaxers

Relaxers straighten curly hair by permanently breaking and reforming bonds.

Types of Relaxers

How Relaxers Work

1. Hydroxide ions break disulfide bonds
2. Bonds convert to lanthionine bonds (cannot be reversed)
3. Hair is smoothed and rinsed
4. Neutralizing shampoo restores pH

Critical Safety Note: Hydroxide relaxers cause a permanent chemical change called lanthionization. This process CANNOT be reversed. Hair cannot be permed after hydroxide relaxer treatment.

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Product Safety

Patch Testing

Always perform a patch test before:

• Hair color services
• Chemical treatments on new clients
• Any product the client hasn't used before

Procedure:

1. Apply small amount behind ear or inner elbow
2. Wait 24-48 hours
3. Check for redness, swelling, itching

Chemical Safety Guidelines

Incompatible Chemicals

Never combine:

• Hydroxide relaxers and thio products
• Metallic salts and oxidizing color
• Different brand chemical systems (unless verified compatible)