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This figure demonstrates how vaginal acidity inactivates pathogens without injuring the vaginal mucosa.

Acid-sensitive pathogens (viruses, bacteria or infected cells) are surrounded by vaginal acidity (hydrogen ions shown as H+ in diagram) and acidified and killed. In contrast, epithelial cells are protected by a layer of mucus, and the small amount of acid that leaks in is easily passed on to the underlying tissue and carried away by the blood.