Unrelieved pressure, however, can lead to ulcer development, beginning with a red mark that won't blanch and then ends with deep tissue destruction. Thus, a red mark that won't go away is the first sign a pressure sore is developing. Many pressure sores go unnoticed for long periods because they begin at the bone or muscle and progress upward. This means underlying tissue can be severely damaged before the skin turns red. Although pressure sores can develop over any bony prominence pressing against the mattress or chair, the areas that are the most prone to tissue breakdown are the bony prominences of the vertebrae in the lower spine, tailbone and hip bones.
Poor circulation can result from lying or sitting in one position for too long.
Improper positioning can also hamper blood flow to any body part. Prolonged sitting on an unpadded surface can obstruct the large blood vessels behind the knees, as well as damage the nerves, causing loss of sensation. Impaired blood flow can also lead to blood clot formation. Lack of fluid intake may increase the risk of clotting of the blood. Although serious, this complication is usually preventable.