The vagina has a natural protective layer which is acidic in nature, to help prevent infection. This layer is maintained when good bacteria called lactobacilli produce lactic acid (or milk acid), which maintains the acidic environment at a ph value of 3.5 to 4.5. This promotes the growth of lactobacilli, inhibiting the presence of harmful bacteria and preventing infection. Therefore, the vagina takes care of itself by continuously producing secretions to provide lubrication.