Hair Anatomy Overview

Hair Anatomy Overview

• Hair is a filamentous outgrowth of the skin, primarily composed of keratinized cells.
• It grows from a follicle located in the dermis, a layer of skin beneath the epidermis.
• The follicle is a complex structure that plays a vital role in hair growth, structure, and maintenance.

Hair Follicle Components

• Hair follicle: Encloses the hair root and associated structures.
• Hair root: The part of the hair embedded within the follicle.
• Hair shaft: The portion of the hair that projects above the skin's surface.
• Hair bulb: The base of the follicle, containing the papilla and matrix.
• Hair papilla: A connective tissue projection into the hair bulb that contains blood vessels and nerve endings, providing nutrients to the hair matrix.
• Hair matrix: A layer of actively dividing cells that produce the keratin proteins forming the hair shaft.
• Arrector pili muscle: Connects the follicle to the surrounding dermis, and controls hair follicle elevation, causing "goosebumps" when contracted.
• Sebaceous glands: Associated with hair follicles, producing sebum, an oily substance that lubricates and protects the hair and skin.
• Sensory nerves: Present in the follicle, contributing to touch perception related to hair movement.
• Blood vessels: Within the papilla provide nutrition to the hair matrix.

Hair Shaft Structure

• Cuticle: The outermost layer of the hair shaft, composed of overlapping scales, which, when correctly aligned, protects the hair. Damage to the cuticle can lead to split ends.
• Cortex: The middle layer of the hair shaft, containing most of the hair’s pigment. This layer is responsible for the hair's color and strength.
• Medulla: The innermost layer of the hair shaft, often less developed or absent in fine hair. This layer is primarily composed of loosely arranged keratin cells.

Hair Growth Cycle

• Hair follicles go through alternating phases of growth (anagen), transition (catagen), and rest (telogen).
• Anagen (growth phase): The active phase of hair growth. The hair matrix continuously produces new keratinized cells, pushing the hair shaft upwards. This phase varies in duration depending on factors.
• Catagen (transition phase): The brief transition phase between active growth and rest. The follicle shrinks, and cell division slows.
• Telogen (resting phase): The resting phase where hair is detached from the follicle. In this phase, the follicle is largely inactive and shedding of old hair occurs.

Hair Color

• Hair color is determined primarily by melanin, a pigment produced by melanocytes within the hair matrix.
• Eumelanin produces brown, black shades of hair.
• Pheomelanin produces red and blonde shades of hair (or mixtures).
• The interplay of these pigments dictates the final hair color.

Factors Affecting Hair Growth and Structure

• Genetics: Predisposition to hair growth rate, color, and texture is largely determined by heredity.
• Hormones: Hormonal factors, such as androgens, play a role in hair growth and distribution, particularly in males and during puberty.
• Nutrition: Proper nutrition, particularly protein intake, supports hair growth.
• Underlying health conditions: Certain medical conditions can affect hair growth and density.
• External factors: Chemical treatments, harsh styling techniques and environmental factors can damage hair.

Clinical Considerations

• Conditions affecting hair include:
  • Alopecia (hair loss): Various forms of hair loss can occur relating to factors above.
  • Trichotillomania (hair-pulling disorder): A mental health condition.
  • Hair shaft disorders can affect hair health.