Hair

• Composed mainly of keratin

Structure of hair:

• Hair shaft:

  • visible part of hair + extends above skin

  • has 3 layers

    • Cuticle

      • outermost layer

      • made of overlapping dead keratinized cells→ protect inner layers + shine

    • Cortex

      • middle layer

      • Strength + color to hair

      • Contains chains of keratin + melanin

    • Medulla

      • innermost layer

      • absent in finer hair

      • function is not well understood

      • may play a role in hair structure

  • Hair Root:

    • embedded in hair follicle

    • contains living cells that divide and grow to produce new hair

  • Hair Follicle:

    • sheath that surrounds the hair root

    • extends down into dermis

    • lined with a layer of epithelial cells

    • contains specialized structures (hair bulb)

  • Hair Growth Cycle

    • Anagen Phase:

      • active growth (2-7 years)

      • cells in hair bulb rapidly divide, producing new hair

      • length of phase determines how long the hair can grow

    • Catagen Phase:

      • short transitional phase (2 to 3 weeks)

      • hair growth slows, hair follicle shrink

      • lower part of the hair bulb dies → reduction in hair length

    • Telogen Phase:

      • resting phase (3 months)

      • hair is not growing

      • hair follicle is inactive

      • hair may fall out end phase, new hair begins to grow in the follicle, starting cycle

    • Types of Hair

      • Terminal Hair:

        • thick, long hair found on:

          • scalp

          • face (such as beards)

          • body (such as underarms and pubic regions)

        • darker and coarser than other hair types

      • Vellus Hair:

        • "peach fuzz"

        • fine

        • short

        • light-colored

        • covers most of the body

        • helps regulate body temperature.

      • Lanugo:

        • soft & fine

        • cover fetus in the womb

        • sheds before birth

• Functions of Hair

  • Protection → sensitive areas

  • Sensation → surrounded by nerve endings, vital for body’s response to environmental changes.

  • Thermoregulation → releasing & trapping air

  • Aesthetic and Social Functions → appearance & identity

    Common Hair Disorders

    • Alopecia → hair loss in patches + thinning of hair

    • Dandruff → flaking skin (overgrowth yeast on scalp)

    • Hirsutism → excessive hair growth in women in areas associated with male hair patterns (related to hormonal imbalances)

    • Hair Shaft Disorders → brittle hair, split ends, hair breakage