. MRSA
Where it lives: Warm and moist areas like your nose, armpits and groin.
What it does: Methicillin-Resistant Staphylococcus Aureus is one of the most common super-bugs, or antibiotic-resistant organisms, and killed almost 20,000 Americans in 2005. Once found only in hospitals, outbreaks are now happening in places like gyms and schools. It's even been found on supermarket meats!
How to get rid of it: If you notice spreading sores or an infection that isn't healing, see your doctor to get tested, then treated with specific antibiotics or ointments. To avoid it, cut down on unnecessary antibiotic use, shower immediately after you hit the gym, cover up your cuts and scrapes, and don't pick your nose!