Candidiasis, also known as vaginal yeast infections, is a common condition that occurs when the balance of bacteria and yeast cells in the vagina changes. As the yeast cells multiply, it causes itching, swelling and irritation. While sometimes, symptoms can be treated within a few days, it can take up to two weeks in some severe cases. Vaginal yeast infections are not considered a sexually transmitted infection, but sexual contact can spread them. However, women who are not sexually active may also get them.