What causes a vaginal yeast infection?
Vaginal yeast infections occur when new yeast is introduced into the vaginal area, or when there is an increase in the quantity of yeast already present in the vagina relative to the quantity of normal bacteria. For example, when the normal, protective bacteria are eradicated by antibiotics (taken to treat a urinary tract, respiratory, or other types of infection) or by immunosuppressive drugs, the yeast can multiply, invade tissues, and cause irritation of the lining of the vagina (vaginitis).
Vaginal yeast infections can also occur as a result of injury to the inner vagina, such as after chemotherapy. Also, women with suppressed immune systems (for example, those taking cortisone-related medications such as prednisone) develop vaginal yeast infections more frequently than women with normal immunity. Other conditions that may predispose women to developing vaginal yeast infections include diabetes, pregnancy, and taking oral contraceptives. The use of douches or perfumed vaginal hygiene sprays may also increase a woman's risk of developing a vaginal yeast infection.
A vaginal yeast infection is not considered to be a sexually transmitted disease (STD), since Candida may be present in the normal vagina, and the condition does occur in celibate women. However, it is possible for men to develop symptoms of skin irritation of the penis from a yeast infection after sexual intercourse with an infected partner, although this is not always the case.