A vaginal yeast infection (vaginal candidiasis) is an overgrowth of Candida yeast, which normally lives harmlessly in small amounts. It typically causes intense vaginal and vulval itching and a thick, white, "cottage cheese" discharge that usually doesn't smell strong.
Triggers include recent antibiotics, pregnancy, uncontrolled diabetes and hormonal changes. Uncomplicated cases often respond to over-the-counter antifungals, but see a clinician for a first episode, recurrent infections, in pregnancy, or if you're unsure — it's easily confused with BV (see yeast infection vs BV and the full yeast infection guide).