Yeast Infection Cause - Version 2.0 Searching For The Yeast Infection's Cause? A yeast infection is an overgrowth of yeast in any area of the body. Yeast infections are also called thrush (usually when referring to the mouth and digestive tract), and candida (candida is the specific name of bacteria causing yeast infections). There is no single yeast infection cause. There are many things that can lead to yeast infections but the most common causal explanations are: a decrease in the acidity of your vagina due to the use of contraceptives, antibiotics, pregnancy, and menstruation (because blood is an alkaline, basic). All of these things alter hormone levels in the body causing changes in the vaginal environment and making it the ideal place for fungus to grow and thrive. Vaginal candidiasis is not referred to as a sexually transmitted disease, however, you can contract if from your partner if they have a yeast infection.