"The first several layers of the skin are like a castle wall protecting the athlete from outside marauders, " Adams says.

CNN: Germ warfare moves to the gym

Worms can get through the intestinal wall and move around under skin tissues.

CNN: Rare tropical disease close to eradication

When a stray bomb hit the south wall of the citadel, sending up clouds of smoke and ash and shattering bits of rubble into his skin, his heart should have stopped.

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