Sweating is a good thing. It's a means of toxin elimination just like urination. Infact wee and sweat are very similar substances. Sweating also helps to regulate temperature but I don't think that is the issue here (you can sweat heavily but not smell bad IYKWIM just as long as you don't stew in it 'cos bacteria love sweat)... it's more what is in the sweat. Does he have a high protein diet? (eat a lot of meat) Red meat eaters tend to have strong smelling sweat. Because eating animals at the end of the food chain can mean more complex things to eliminate via sweat. I stopped eating red meat at the age of 18 and I noticed that people smelled differently. It's not necessarily a "bad" smell, just stronger.
Does his wee smell strongly too, is it dark? That could indicate that a good flushing out is needed. I try to wee "clear" once a week. Not always easy to do LOL but very good for the system.