Cosmetology

Properties of Hair & Scalp

Hair Structure

Thier are five main structures of a hair root.

• Hair Follicle: the tube-like depression or pocket in the skin or scalp that contains the hair root
• hair bulb: lowest part of a hair strand; the thickened, club-shaped structure that forms the lower part of the hair root.
• dermal papilla: a small, cone-shaped elevation located at the base of the hair follicle that fits into the hair bulb
• arrector pili muscle: the small, involuntary muscle in the base of the hair follicle
• sebaceous glands: the oil glands in the skin that are connected to the hair follicles

Their are three main layers or Structures of Hair Shaft

• Hair cuticle: outermost layer of hair; consisting of a single, overlapping layer of transparent, scale-like cells that look like shingles on a roof.
• cortex: middle layer of the hair; a fibrous protein core formed by elongated cells containing melanin pigment
• medulla: innermost layer of the hair that is composed of round cells; often absent in fine and naturally blond hair.

Two types of hair found on the body

Vellus hair: short, fine, unpigmented, downy; appears on parts of the body that are normally considered hairless (forehead, eyelids, bald scalp); almost never has a medulla; helps with the evaporation of perspiration; women normally retain 55% more vellus hair than men

Terminal Hair: long, coarse, pigmented hair found on the scalp, legs, arms, and bodies of both males and females; it usually has a medulla

Growth Cycles of the hair

anagen phrase: also known as the growth phrase; new hair is produced

catagen phrase: brief transition period between the growth and the resting phases of a hair follicle; signals the end of the anagen phase; lasts from one to two weeks.

telogen phrase: also known as the resting phrase; final phase in the cycle; lasts  until the fully grown hair is shed

Hair growth patterns

Hair stream: is hair flowing in the same direction. It is the result of the follicle sloping in the same direction.

Whorl: is hair that forms in a circular pattern, as on the crown.

Cowlick: is a tuft of hear that stands straight up. Usually more noticeable on the hairline.

Chemical Composition of Hair

Keratinization: process by which newly formed hair cells in the hair bulb mature, fill with keratin, move upward, lose their nucleus and die

Keratin: a fibrous protein that grows from cells originating within the hair follicle

COHNS elements: Major elements that make up hair: Carbon, Oxygen, Hydrogen, Nitrogen, and Sulfur

amino acids: units that are joined together end-to-end like pop beads by strong, chemical peptide bonds to form the polypeptide chains that comprise proteins

peptide bond: also known as end bond; chemical bond that joins amino acids to each other, end-to-end, to form polypeptide chain

polypeptide chain: a long chain of amino acids linked by peptide bonds

proteins: long, coiled complex polypeptides made of amino acids

Side Bonds of the cortex: link the polypeptide chains (long chain of amino acids linked together by peptide bonds) together; responsible for the strength and elasticity of human hair

• hydrogen bond: weak, physical cross-link bond that is easily broken by water or heat
• salt bond: weak, physical cross-link bond that is broken by alkaline or acidic solutions
• disulfide bond: strong, chemical side bond; can be broken by extreme heat, some high-temp styling tools, permanent waves and chemical relaxers