Hair and Scalp Properties

Rationale and Importance of Hair and Scalp Analysis

• Cosmetologist Responsibilities:
  • Protecting the health and integrity of clients' hair and scalp is a fundamental responsibility.
  • Requires a thorough understanding of hair composition and how hairstyling and chemical services alter hair.
• Key Reasons to Study Hair and Scalp Properties:
  • Baseline Analysis: Analyzing the hair and scalp is a critical first step to delivering services that maintain their overall health and integrity.
  • Safer, Smarter Services: Understanding how the hair structure is formed and how both hairstyling and chemical services alter hair leads to safer and more effective services.
  • Targeted Recommendations: Identifying hair growth cycles and differentiating between common and uncommon hair loss enables cosmetologists to recommend appropriate hair loss treatments to clients.

Foundations of Trichology and the Integumentary System

• Definition of Trichology:
  • The scientific study of hair, including its diseases and care.
  • Derived from the Greek word trichos, meaning "hair", and the suffix ology, meaning "the study of".
• The Integumentary System:
  • Composed of the hair, skin, nails, and glands.
  • While hair is no longer essential for human warmth and protection, it plays a major role in human psychology.
• Primary Structural Divisions of Hair:
  • Hair Root: The portion of hair located below the epidermis (the outer layer of the skin).
  • Hair Shaft: The portion of hair that projects above the epidermis.

Hair Root Structures and Functions

• Living Portion of the Hair:
  • Situated below the skin surface.
  • Consists of three primary structures: the hair follicle, hair bulb, and dermal papilla.
• Hair Follicle:
  • A tube-like structure located in the skin or scalp that surrounds and anchors the hair strand in the skin.
  • Distribution: Present across the skin, but specifically absent from the palms of the hands and the soles of the feet.
  • Associated Structures: Attached to the arrector pili muscles and sebaceous glands.
• Hair Bulb:
  • Located at the base of the hair follicle.
  • Features a distinct bulb-shaped structure.
  • Contains living cells responsible for forming the hair strand.
• Dermal Papilla (Plural: Dermal Papillae):
  • Also referred to as the hair papilla.
  • A cone-shaped elevation situated at the base of the hair bulb.
  • Contains dermal blood vessels that supply the necessary nutrients to enable hair growth.
• Arrector Pili Muscle:
  • An involuntary muscle located in the dermis that attaches directly to the hair follicle.
  • Function: When contracted, it causes the hair strand to stand upright, resulting in goosebumps.
• Sebaceous Glands:
  • Glands attached directly to the hair follicle.
  • Produce a fatty or oily substance known as sebum (or oil).
  • Function: Sebum lubricates and conditions both the hair and skin.
• Anatomical Layers of Skin Surrounding the Root:
  • Epidermis: Outer layer of skin.
  • Dermis: Inner layer containing dermal blood vessels, arrector pili muscle, and sebaceous glands.
  • Subcutaneous Layer: Deep layer situated beneath the dermis.

Hair Shaft Structure and Main Layers

• Definition of the Hair Shaft:
  • Also known as the hair strand or hair fiber.
  • Represents the nonliving portion of hair that extends beyond the skin or scalp.
• Three Main Layers of the Hair Shaft:
  • Hair Cuticle:
    • The outermost layer of the hair shaft.
    • Formed from individual cells that overlap each other, similar to shingles on a roof.
    • Composed of $6\text{ to }10$ layers of cells.
    • Function: Acts as a protective barrier for the inner cortex.
    • Behavior: Lies flat in healthy hair; softens and swells during chemical services, allowing chemicals to penetrate into the cortex layer.
  • Cortex:
    • The middle, fibrous protein layer of the hair.
    • Function: Gives hair its strength, elasticity, and color.
    • Weight: Accounts for approximately $90\%$ of the total weight of the hair.
  • Medulla:
    • Also known as the hair's pith or core.
    • Distribution: Not found in all hair types.
    • Generally present in coarse hair and absent in fine hair.
    • Special Distinction: Beard hair always contains a medulla.

Chemical Composition and Keratinization

• Chemical Composition Breakdown:
  • Hair is composed primarily of protein, making up approximately $90\%$ of its total structure.
  • The remaining $10\%$ consists of a combination of water, lipids, and trace minerals.
  • Building Blocks: Protein structure is formed by amino acids.
• The Keratinization Process:
  • Living cells in the hair bulb undergo keratinization to form the nonliving hair shaft.
  • Step 1: Newly formed cells mature and fill up with a fibrous protein called keratin.
  • Step 2: Cells migrate upward, lose their cell nucleus, and die.
  • Step 3: As the hair strand emerges from the scalp, its cells are completely dead and fully keratinized.
• The COHNS Elements:
  • The five major chemical elements that make up human hair, skin, and nails.
  • Carbon: Makes up $51\%$ of average hair.
  • Oxygen: Makes up $21\%$ of average hair.
  • Hydrogen: Makes up $6\%$ of average hair.
  • Nitrogen: Makes up $17\%$ of average hair.
  • Sulfur: Makes up $5\%$ of average hair.

Chemical Bonds and Structural Helix of Hair

• Peptide Bonds:
  • Also known as end bonds.
  • Extremely strong chemical bonds that join amino acids end to end.
• Polypeptide Chains:
  • Long chains formed when amino acids are linked together end to end by peptide bonds.
• Helix Configuration:
  • Polypeptide chains form a spiral configuration known as a helix.
• Side Bonds Associated with the Helix:
  • Salt Bond: Side bond holding polypeptide chains together.
  • Disulfide Bond: Strong chemical side bond within the spiral helix.
  • Hydrogen Bond: Physical side bond within the helix.

Review Check-In Questions and Responses

• Question 1: Describe three ways studying hair and scalp properties benefits you as a cosmetologist.
  • Response:
    1. Conducting hair and scalp analysis is a vital first step in delivering services that maintain hair health and integrity.
    2. Understanding hair formation and the impact of styling and chemical services promotes safer and smarter service delivery.
    3. Differentiating between normal and abnormal hair loss along with hair growth cycles enables accurate recommendations for hair loss treatments.
• Question 2: Name and describe the structures of the hair root.
  • Response:
    • Hair Follicle: Tube-like structure in the skin/scalp that anchors the hair strand (absent on palms and soles).
    • Hair Bulb: Bulb-shaped structure at the base of the follicle containing living cells that form hair.
    • Dermal Papilla: Cone-shaped elevation at the base of the hair bulb containing dermal blood vessels providing nutrients for growth.
    • Arrector Pili Muscle: Involuntary dermis muscle attached to the follicle that contracts to produce goosebumps.
    • Sebaceous Glands: Glands attached to the follicle that secrete sebum (oil) to lubricate hair and skin.
• Question 3: Which parts of the hair are living?
  • Response: The living portions of hair are located below the skin surface and comprise the hair follicle, hair bulb, and dermal papilla.
• Question 4: Name and describe the three layers of the hair shaft.
  • Response:
    1. Cuticle: Outermost layer consisting of $6\text{ to }10$ overlapping cell layers that protect the cortex; swells and softens during chemical services.
    2. Cortex: Fibrous protein layer comprising $90\%$ of hair weight, responsible for strength, elasticity, and color.
    3. Medulla: Core or pith of the hair shaft; present in coarse hair and beard hair, but typically missing in fine hair.
• Question 5: What type of hair will always have a medulla?
  • Response: Beard hair will always contain a medulla.