What causes bad breath? I had a bad stomach and bad breath yesterday - could they be linked?

It's possible in incredibly extreme cases, but for most people halitosis arises mainly in the mouth and the so-called oropharynx, the early part of the throat. I think people like to think that they have really serious terrible problems, when in fact all they have to do is clean their teeth. There is a guy in Israel who has actually started a halitosis research institute, and he wanted to know if bad breath was in the eye, or nose even, of the beholder, or whether it was a psychological thing where people think they've got bad breath, and they haven't - delusional halitosis as it is known. He went round sniffing the breath of 200 people or so, in order to define what kinds of bad breath there are and what causes it.