DEFENSE ONE
The normal; vaginal discharge continuously cleans the vagina .
DEFENSE NUMBER TWO
There are so called good germs that do not harm our bodies. When they are in the majority . they compete and suppress possible harmful organisms and protect the vagina against invaders.
In adult female during her reproductive years, the cells lining the vagina contains large amount of glycogen(a starch like substance) When these cells die and are shed, some of the good bacteria uses the glycogen as a source of energy and produce lactic acid as by product. Lactic acid is a very weak acid and doesn't irritate the vagina. The lactic acid make the vagina slightly acid. The acid makes the vaginal environment unfavorable for most harm full germs. The lactic acid keeps harmful germs out.
The most important defense is the presence of lactic acid producing germs. The cells lining the adult vagina contains glycogen ( a type of starch). The cells on the surface of vaginal continually die and are replaced by new cells. The lactic acid producing bacteria ( germs) use the glycogen in these cells as energy and while fermenting the glycogen= they produce lactic acid. Lactic acid is a weak acid and won't damage the vaginal wall, but it makes the vagina slightly acid and creates and creates an unfavorable environment for other germs to thrive in.