Table 1.

Cutaneous barrier functions

Barrier	Roles	Effectors
Permeability	Prevents excess water loss, harmful chemicals, allergens, and microbial pathogens; Maintains body temperature	Components of skin structure
Antimicrobial	Protects against multiple pathogens, e.g, Gram-positive and Gram-negative bacteria, fungi, and some viruses	Acidic pH (<5.5); Sphingoid bases; Innate immune elements, including antimicrobial peptides
Antioxidant	Protects skin from oxidative stress	α-/γ-tocopherol Vitamin C and E Certain flavonoids
UV	Protects skin from UV light-mediated DNA damage, and oxidative stress	Urocanic acid Structure components, including sphingolipids