A Bartholin's cyst occurs when a Bartholin's gland within the labia becomes blocked. Small cysts may result in minimal symptoms. Larger cysts may result in swelling on one side of the vagina, as well as pain during sex or walking. If the cyst becomes infected, an abscess can occur, which is typically red and very painful. If there are no symptoms, no treatment is needed. Bartholin's cysts affect about 2% of women at some point in their life. They most commonly occur during childbearing years.