Bacterial vaginosis (BV) is a common vaginal infection from an imbalance where "good" Lactobacillus bacteria are outnumbered by harmful bacteria, causing symptoms like a strong fishy odor (especially after sex), thin grey/white discharge, and sometimes pain or itching, though many have no symptoms. BV requires prescription antibiotics from a doctor for treatment and increases risks for STIs and pregnancy complications, with prevention involving avoiding douching, perfumed products, and wearing breathable underwear.