Blood is alkaline, meaning it has a pH of about 7.4. Each time there is blood in the vagina (e.g. from menstruation, spotting, blood traces after surgery) the pH in the vagina shifts temporarily to a higher value. Semen (or seminal fluid) is also alkaline to enable sperm motility. Amniotic fluid and lochia (the vaginal discharge after giving birth) are also alkaline body fluids. The lactic acid produced by the lactobacilli in the healthy vagina normally balances out alkaline body fluids, but if the vaginal flora is weakened or disturbed, this compensation is delayed or does not occur. The subsequent shift in the pH of the vagina to above 4.4 can favour the growth of disease-causing pathogens.