Pressure ulcers or bedsores arise if you have an inadequate supply of blood flow to the skin in a particular region. They form when your skin and soft tissue presses against a harder surface such as chair or bed for a long time. This pressure reduces the blood flow to the area. Lack of blood supply damages the skin tissues resulting in pressure ulcers. The most typical reason for a pressure sore is the lack of movement. So, it is common in people who are moving in wheelchairs or lying in a bed. People who are overweight or underweight can also develop pressure ulcers. It also happens to people who are not able to control their bowels or bladder and people who spend a lot of time in one position.