I want to talk about tonsil stones, if you have never smelled someone's breath with tonsil stones, you are very lucky. This is not typical bad breath, it's very foul and you can smell it even standing a few feet away from someone. It's disgusting because it's really old food debris that got stuck inside pits of the tonsils (sometimes other areas of the back of the throat). The stones stay there and get bigger and smell worse over time. If you have ever smelled plaque that was scrapped off your tooth at the dentist, that's what it smells like, only worse somehow. No amount of brushing or chewing gum helps because the smell is coming from the stones themselves, so Ian's breath will still stink even if he brushes his teeth 3 times a day.
The only way to get rid of that smell is to get rid of the stones themselves. There are videos online that discuss how you can get rid of them yourself. But if the stones have been there a while and are really bad, you have to go to a dentist or ENT doctor so they can squeeze every one out. Sometimes it's bad enough that the entire tonsils are rotten and have to be removed. Since Ian's hygiene has been an issue for years, I'm assuming his tonsil stones are horrific and that he will need professional help to get rid of them.