What is the primary cause of decompression sickness experienced by divers?

The primary cause of decompression sickness, often referred to as "the bends," is related to rapid changes in pressure experienced when divers ascend too quickly after spending time at depths underwater. During a dive, nitrogen from the air dissolves into the body's tissues due to the increased pressure. If a diver holds their breath during ascent, the expanding air within the lungs can result in lung over-expansion injuries and subsequent release of nitrogen bubbles into the bloodstream. These bubbles can block blood flow and cause severe pain, as well as damage to various tissues and organs.

In contrast, while excessive water intake and uncontrolled breathing exercises can lead to other issues, they do not directly contribute to the physiological conditions that cause decompression sickness. Similarly, a slow descent underwater helps to prevent the nitrogen from dissolving excessively in the body's tissues, which is crucial for avoiding this type of sickness. Thus, the act of holding one's breath during ascent is the critical factor that can lead to the dangerous complications associated with decompression sickness.