No. Wearing polyester or other nonorganic materials (meaning most anything other than cotton) will not cause bladder infections. However, since they don't let your privates breathe, you're at risk for vaginal yeast and bacterial infections. You're much better off wearing all-cotton undies and thongs whenever you can. If you absolutely must have undergarments made of silky strands, make sure the crotch is lined with a cotton strip. And white underwear is really best, since dyes can cause problems, too.

— Kristin Kemp