their are certain parts of teh body that must remain acidic or opportunistic organisms like candida can flourish.
the stomach is one, without sufficient stomach acidity you wouldnt able to digest properly, and candida would go from its normal form to the fungal pathogen form.
The vagina and so on is the same, without sufficient acids, you will get yeast infections etc. Which is why natural yogurt is touted as a cure. The good bacteria produce acids that keep these organisms at bay.