What gas is primarily responsible for decompression sickness?

Decompression sickness, often referred to as "the bends," is primarily caused by nitrogen. When a diver descends underwater, they are exposed to increased pressure, which causes nitrogen from the breathing gas to dissolve into the body's tissues and bloodstream. As the diver ascends, the pressure decreases, and if the ascent is too rapid, the nitrogen comes out of solution too quickly, forming bubbles that can lead to various symptoms and complications associated with decompression sickness.

Whereas oxygen, helium, and carbon dioxide play important roles in diving and gas physiology, they do not primarily contribute to the formation of bubbles in tissues during rapid decompression. Oxygen is present in the breathing mix but is not a factor in decompression sickness itself. Helium is often used as a less soluble alternative in deep diving to reduce nitrogen absorption and is not associated with decompression sickness in the same way. Carbon dioxide is a product of metabolism and can contribute to other physiological issues, but it is not responsible for decompression sickness. Therefore, nitrogen's role as the gas that dissolves and later forms bubbles during rapid ascents makes it the primary agent linked to this condition.