A condition in which too much yeast grows in certain areas of the body and causes symptoms and disease. Small amounts of yeast normally live on the skin and in other parts of the body, such as the mouth, throat, and vagina. Sometimes, too much yeast can grow in these areas and cause infection. Yeast infections may also occur in the blood and spread throughout the body, but this is rare. Certain conditions, such as a weakened immune system, diabetes, pregnancy, hormone changes, and stress, and use of certain medicines may increase the risk of yeast infection.