Hair Anatomy (Cuticle, Cortex, Medulla) and the Science of Goosebumps (Piloerection)

Hair Structure

• Cuticle: Overlapping keratin scales; protects cortex; determines shine/smoothness.
• Cortex: Bulk of hair; keratin bundles + melanin; provides strength, elasticity, color.
• Medulla: Central core (absent in fine hair); loosely packed cells; function unclear.

Goosebumps (Piloerection)

Triggered by contraction of the arrector pili muscle (smooth muscle attached to hair follicle). Causes:

• Cold: Sympathetic response; traps air for insulation (vestigial in humans).
• Fear/excitement (strong emotions): Adrenaline-mediated; part of fight-or-flight.

Clinical Note

Usually benign. Persistent or unusual piloerection may accompany hypothyroidism, opioid withdrawal, autonomic dysreflexia, or temporal lobe seizures.