Chp 11 Cosmetology Written Study Guide: Properties of Hair and Scalp

Structures of the Hair Root

• Hair Follicle: A tube-like depression or pocket in the skin or scalp that contains the hair root.

• Hair Bulb: The lowest area or part of a hair strand; a thickened, club-shaped structure that forms the lower part of the hair root.

• Dermapapilla / Dermapapillae: Small, cone-shaped elevations located at the base of the hair follicle that fit into the hair bulb. They contain the blood and nerve supply that provides the nutrients needed for hair growth.

• Erector Pili Muscle: Minute involuntary muscle fibers in the skin inserted at the base of the hair follicle. Fear or cold causes this muscle to contract, making the hair stand straight up and resulting in goosebumps.

• Sebaceous Glands: The oil glands of the skin connected to the hair follicles. They secrete an oily substance called sebum, which lubricates the hair and skin.

Structures of the Hair Shaft

• Hair Cuticle: The outermost layer of the hair. It consists of a single overlapping layer of transparent, scale-like cells that overlap like shingles on a roof. It lies tightly against the cortex, providing a barrier that protects the inner structure of the hair, and is responsible for creating the shiny, smooth, silky feel of healthy hair.

• Cortex: The middle layer of the hair. It is a fibrous protein core formed by elongated cells containing melanin pigment.

• Medulla: The innermost layer of the hair shaft composed of round cells. Very fine and naturally blonde hair may not possess a medulla, whereas thick, coarse hair and beard hair always contain a medulla.

Hair Chemical Composition and Keratinization

• Protein Content: Hair is approximately $90\%$ protein, which is composed of long chains of amino acids.

• Conn's Elements: The major elements that make up human hair, which are also found in skin and nails:

  • Carbon

  • Oxygen

  • Hydrogen

  • Nitrogen

  • Sulfur

• Keratinization: The process where living cells originating within the hair follicle mature as they begin their journey upward through the hair follicle.

• Keratin: A fibrous protein that fills newly formed cells as they mature. As cells fill with keratin on their upward movement, they lose their nucleus and die.

• Amino Acids and Peptide Bonds: Amino acids are units that join together end-to-end like beads to form long chains of protein.

  • Peptide Bonds: The strong chemical bonds that join amino acids together, also referred to as end bonds.

Polypeptide Chains and Cortex Side Bonds

• Polypeptide Chain: A long chain of amino acids linked together by peptide bonds. Proteins are long, coiled, complex polypeptides made of amino acids.

• Helix: The spiral shape of a coiled protein, created when polypeptide chains intertwine with each other.

• Side Bonds of the Cortex: The cortex is made up of millions of polypeptide chains cross-linked like the rungs on a ladder by three distinct types of side bonds responsible for the strength and elasticity of hair:

  • Hydrogen Bond: A weak, physical, cross-link side bond easily broken by water or heat. Although weak individually, their vast abundance accounts for approximately $\frac{1}{3}$ of the hair's strength.

  • Salt Bond: A weak, temporary cross-link side bond broken by changes in pH (such as strong alkaline or acidic solutions). Accounts for approximately $\frac{1}{3}$ of the hair's overall strength.

  • Desulfide Bond: A strong chemical side bond that joins the sulfur atoms of two neighboring cysteine amino acids to create cystine. Cystine joins together two polypeptide strands. Desulfide bonds account for approximately $\frac{1}{3}$ of overall hair strength.

  • Desulfide bonds are not broken by water; they are broken by permanent waves and chemical hair relaxers to alter the hair's shape.

  • Lanthanin Bonds: Created when hydroxide relaxers break and convert desulfide bonds when the relaxer is rinsed from the hair.

Hair Pigment and Wave Patterns

• Melanin: Tiny grains of pigment located within the cortex that yield natural hair color:

  • Eomelanin: Provides dark brown and black color to hair.

  • Pheomelanin: Provides natural hair colors ranging from red and ginger to yellow-blonde tones.

  • Natural Mixtures: A person's natural hair color is produced by a mixture of these pigments.

  • Gray Hair: Contains only a few scattered melanin granules.

  • White Hair: Does not contain any melanin granules.

• Wave Pattern: Refers to the shape of the hair strand, which is determined by genetics and can vary from strand to strand:

  • Straight

  • Wavy

  • Curly (curly hair is oval in shape)

  • Extremely curly

Types of Hair and Growth Cycles

• Vela's Hair (Vellus Hair / Lanugo): Short, fine, downy, unpigmented hair covering most of the body, with the exception of the palms of the hands and soles of the feet.

• Terminal Hair: Long, thick, pigmented hair found on the scalp, legs, and arms. It is coarser than vellus hair, usually contains a medulla, and is pigmented (except gray hair).

• Hair Growth Cycles: Each complete growth cycle consists of three repeating phases:

  • Anagen Phase: The active growing phase of the hair.

  • Catagen Phase: The transition phase that ends the growth phase, lasting $1\text{ to }2\text{ weeks}$. The follicle canal shrinks and detaches from the dermapapilla.

  • Telogen Phase: The resting phase following catagen, lasting $3\text{ to }6\text{ months}$.

Disorders of the Hair and Scalp

• Hair Shaft Disorders:

  • Canadies: Technical term for gray hair resulting from the loss of natural pigment in the hair.

  • Ringed Hair: Characterized by alternating bands of gray and pigmented hair throughout the length of the hair strand.

  • Hypertrichosis: Characterized by the growth of terminal hair in areas of the body that normally grow vellus hair.

  • Tricapatillosis: Technical term for split ends.

  • Tritorhexis Nodosa: Knotted hair; a dry, brittle condition involving nodular swellings along the hair shaft where hair breaks very easily.

  • Monilextrics: Condition where hair tends to break between the beads or nodes.

• Types of Abnormal Hair Loss:

  • Androgenic Alopecia: A genetic condition affecting both men and women. In men (male pattern baldness), hair loss can begin in the teens or $20\text{s}$, characterized by a receding hairline and gradual disappearance of hair from the crown and frontal scalp.

  • Alopecia Areata: An autoimmune disorder where hair follicles are attacked by the person's own immune system. White blood cells stop hair growth during the anagen phase.

  • Postpartum Alopecia: Temporary hair loss occurring at the conclusion of pregnancy; hair growth usually returns to normal within $1\text{ year}$ after delivery.

• Scalp Disorders and Infections:

  • Pitoriasis: Technical term for dandruff, characterized by excessive production and accumulation of skin cells.

  • Pityriasis Capitis Simplex: Classic dandruff.

  • Pityriasis Tetodes: A more severe case of dandruff.

  • Fungal Infections:

  • Tinea: Technical term for ringworm; characterized by itching, scales, and painful circular lesions.

  • Tinea Capitis: Ringworm of the scalp; produces red papules or spots at the opening of hair follicles, causing hair to break.

  • Tinea Favossa: Characterized by dry, sulfur-yellow, cup-like crusts on the scalp called scutula.

  • Parasitic Infections:

  • Highly contagious skin disease caused by a parasitic mite that burrows under the skin.

  • Piticulosis Capitis: A contagious condition caused by head lice infesting the hair and scalp.

  • Bacterial Infections:

  • Furuncle: Technical term for a boil; an acute localized bacterial infection of the hair follicle that produces constant pain.

  • Carbuncle: An inflammation of the subcutaneous tissue caused by staphylococci.

  • Folliculitis: Infection of the hair follicle.

Physical Properties of Hair

• Hair Texture: Refers to the diameter of individual hair strands:

  • Coarse Hair: Has the largest diameter.

  • Medium Hair: Most common hair texture; considered normal.

  • Fine Hair: Has the smallest diameter and is more fragile.

• Hair Density: Measures the number of individual hair strands present on $1\text{ square inch}$ of scalp.

• Hair Porosity: The ability of the hair to absorb moisture, directly related to the condition of the cuticle layer:

  • Low Porosity: Considered resistant hair. Chemical services on low porosity hair require a more alkaline solution than on high porosity hair.

  • Average Porosity: Considered normal hair.

  • High Porosity: Result of hair that is over-processed, making it damaged, fragile, and brittle.

• Hair Elasticity: The ability of the hair to stretch and return to its original length:

  • Normal Elasticity: Wet hair with normal elasticity stretches up to $50\%$ of its original length and returns without breaking.

  • Low Elasticity: Hair that breaks easily or fails to return back to its original length.