You know working out is great for your body, your heart, and your mood—but, you have to wonder, does your skin take a beating from all that sweating? Richard G. Glogau, M.D., a clinical professor of dermatology at the University of California at San Francisco, gives his tips for keeping your body's largest organ smooth and fresh—while still honing the rest of that lean, mean, fighting machine.  Rule Number 1: If you've broken a sweat, take a shower. Okay, so this seems obvious, but there are more reasons than you think not to skip that shower after your midday…