Well, I noticed when I'd be spinning my cbb in my ear, and my hand would smell bad...that or the jewelry smells bad. You'll know it for sure when it happens. All you gotta do is keep them clean with regular soap and (in the case of cbr's and the like) get soap on the jewelry and spin it a few times to get the soap into the piercing and clean it out. Make sure you rinse well, too. You don't want dried up soap stuff on there either.
-Keepin' it real since '86