A vaginal yeast infection is irritation of the vagina and the area around it called the vulva (vul-vuh).
Yeast is a type of fungus. Yeast infections are caused by overgrowth of the fungus Candida albicans. Small amounts of yeast are always in the vagina. But when too much yeast grows, you can get an infection.
Yeast infections are very common. About 75 percent of women have one during their lives. And almost half of women have two or more vaginal yeast infections.
This answer is based on source information from the National Women's Health Information Center.