While body odor is most often caused by sweating, there are a whole mess of other things that can make you smell. You can reek of rotten fish or warm baked bread. Either way, those odors are a sign of something amiss.
Yuck! If your workout clothes smell stinky, it might not just be because you're sweating. It can also have to do with what kind of material you are wearing. Surprisingly, natural does not always mean "breathable."