You may want to mention this to his doctor. It's true that some people are just smellier than others - it's their body chemistry. (Would you believe that some people, with a sensitive enough nose, can identify a person's gas by the smell?? eeewwww but true) However, if it's really smelly, it could be an indication of something else. Is this a recent thing or has he been like this for most of his life? That could also indicate if it's just his chemistry or something else.
It wouldn't hurt to just call the doctor during office hours to get an opinion on whether you should worry or not.