Can you pick up a yeast infection from a guy? even if he has no symptoms?

Not usually: Sometimes after sex, the ph of a women's vagina can change which can make a women develop a yeast infection.

Some basics: Yeast is a normal germ found in the digestive tract. Vaginal yeast infections usually arise from cross contamination when the yeast germ crosses over to the vagina from the anus. It can also be a complication of anal sex followed by vaginal intercourse. The glucose contained in the vaginal secretions sustain the growth of yeast. Any form of diabetes increases risk of vaginal thrush.