How does a person's body decompose? The body does not begin to decompose, break down until a person has been dead for at least 24-72 hours. At this point, their internal organs will start to decompose. When a decomposing body starts to decay, it becomes exposed to its surroundings. According to Molly Edmonds, “the Corpse ecosystem really comes into its own a place for germs, insects, and scavengers” If the body is exposed to air it will decompose twice as fast as a body immersed in water and eight times as fast a body buried in soil. The body will take about fifty years for it to fully break down. So as you can see the body takes different times to break down depending on what it is in.