Table 2.

Physiological barriers protecting the vulva.

Vulvar protective barrier/characteristic	Description	Function
Microbiota	Species may include staphylococci, micrococci, diphtheroids, lactobacilli, streptococci, Gram-negative rods and yeasts (non-protective species of faecal origin may also be present) 3	May reduce the proliferation of exogenous pathogens that cause vaginal and urinary tract infections 3
pH	Vulvar pH could be expected to fall between the pH of the skin (pH 4.7) 3 and the vagina (normal pH 4.0–4.5)3,77	Protects against sexually transmitted pathogens 78
Pubic hair	Body hair found in the genital area 79	Contributes to the microenvironment favouring evaporation of pheromones. 42 Moderately protects the genitalia from foreign bodies, bacteria and viruses, and protects skin from friction during intercourse that can lead to dryness, irritation and abrasions79,80
Skin (epithelium)	Vulvar skin: differs from other skin sites in hydration, friction and permeability and is more susceptible to topical agents than forearm skin Vulvar vestibular skin: non-keratinized and therefore likely to be more permeable, and vulnerable to mechanical traumas (e.g. due to friction) than keratinized skin3,81	Provides a physical/mechanical biobarrier 82
Epithelial cells	The cutaneous epithelium of the mons pubis and labia majora exhibits a keratinized, stratified, squamous structure with sweat glands, sebaceous glands and hair follicles. The degree of keratinisation decreases over the clitoris and the outer surface and inner two-thirds of the labia minora. The epidermis of this portion of the labia minora is markedly thinner than that of the labia majora and there are no hair follicles or sweat glands in women of reproductive age 81	Provides a physical barrier 82 and acts as an immunocompetent tissue: Langerhans’ cells are the most common immune cell type in the vulva 81