The air a scuba diver breathes is pressurized to counteract the pressure exerted by the water surrounding the diver’s body. Breathing the high-pressure air causes excessive amounts of nitrogen to dissolve in body fluids, especially the blood. If a diver ascends to the surface too rapidly, the nitrogen bubbles out of the body fluids (much like the way carbon dioxide bubbles out of a soda immediately after the container is opened). This results in a painful and potentially lethal medical condition known as the bends. Why does breathing a mixture of helium and oxygen, rather than air, help divers avoid getting the bends?