Skin's Defense Mechanisms: How Your Epidermis Fights Disease

The skin is a multi-layered, active immune organ—not just a passive barrier.

Physical & Chemical Barriers

• Stratum Corneum: Keratin "bricks" + lipid "mortar" → impermeable shield.
• Desquamation: Continuous shedding removes adhered microbes.
• Acid Mantle (pH 4.5–5.5): Sebum + sweat + urocanic acid → inhibits pathogens.
• Antimicrobial Peptides: Defensins, cathelicidins (LL-37), RNase 7, psoriasin – broad-spectrum killing.
• Sebum: Free fatty acids (sapienic acid) → antibacterial/antifungal.

Immune Surveillance

• Langerhans Cells: Epidermal dendritic cells → capture antigen → migrate to lymph nodes → prime T cells.
• Dermal Dendritic Cells, Macrophages, Mast Cells, γδ T cells, ILC2s: Rapid innate/adaptive responses.

Inflammation & Repair

• Vasodilation, leukocyte recruitment, cytokine cascade.
• Re-epithelialization (keratinocyte migration), granulation tissue, remodeling.

Compromising Factors

Aging, diabetes, steroids, malnutrition, immunosuppression, harsh cleansers, occlusion.