There are lots of bacteria and yeasts and other microbiotics that live inside us every day. Normally, they keep each other in balance and we never notice. Sometimes things get out of balance and one or the other of them begins to overgrow.

That's what yeast infections are. We don't just pick up some yeasts and start growing them - they were there already. Something shifts in our body chemistry (eat too much sugar or not enough vegetables or stress or a thousand possible things) and they start reproducing out of scale. Bacterial infections can be the same way. Something that is normally in there gets out of balance.

Just because "something" shows up doesn't mean that we automatically "got it" from someone else. That said - partners should probably get checked for things together, or at least, get checked. They've told me that men can pick up and carry some of these things without having any problems, and next thing you know, they can plant the wild yeast right back!