Vaginal thrush is mainly caused by an overgrowth of a yeast called Candida albicans. This yeast is naturally present in the body, including the vagina. However, certain factors can lead to its overgrowth and cause an infection. These factors include an imbalance in the microbial environment, the use of antibiotics, a weakened immune system, hormonal changes (like those during pregnancy or the menstrual cycle), uncontrolled diabetes, and other lifestyle factors such as stress and tight clothing.