A bed sore- is an open, ulcerated lesion on any part of the skin while a pressure ulcer- is an ulcer of the underlying soft tissue and it can develop anywhere on the body. Pressure sores usually occur from friction from rubbing against something that is rough or hard. Bed sores are generally caused by too oily, too heavy or too warm bedding. If a bed sore does not heal within 7 days it should be seen a doctor for evaluation.