No, your body cannot explode underwater under normal circumstances. The human body is not designed to explode, regardless of the environment it is in. Explosions typically occur when there is a rapid release of energy that causes a sudden increase in pressure, leading to the rupture or fragmentation of objects.
While water is denser than air, it exerts pressure on the human body at a relatively constant rate. The pressure increases with depth as you descend deeper into the water, but as long as the pressure changes are gradual and within safe limits, the human body can adapt to it without any issues.
However, it's important to note that extreme changes in pressure, such as those experienced in deep-sea diving or if a person rapidly ascends to the surface from a significant depth, can lead to serious medical conditions like decompression sickness (the bends) or lung overexpansion injuries. These conditions can be life-threatening and require proper diving protocols and safety measures to prevent them.