Explore the common causes and treatments of yeast infections, which affect 3 out of every 4 people with a vagina. -- The vagina harbors hundreds of different kinds of microorganisms. Candida yeasts are usually present in small quantities and most of the time, these fungi are harmless. But, under certain conditions, Candida yeasts can cause infections. One species in particular is the usual culprit of vaginal yeast infections. So, how exactly does a yeast infection happen? Liesbeth Demuyser investigates. Lesson by Liesbeth Demuyser, directed by Mette Ilene Holmriis, The Animation Workshop.