Historically, pressure sores have been seen as a nursing problem, and still are to a certain extent today. Nurses therefore need to have a comprehensive understanding of the physiology of the skin to assist them in preventing and treating pressure sores. Despite a great deal of research on the aetiology of pressure sores, their origins are still not fully understood. This article discusses the physiology of the skin and the aetiology of pressure sores. Influences on pressure sore development are multifactorial and tend to be divided into three main categories: extrinsic (e.g. environmental pressure, shear and friction), intrinsic (e.g. general health, age, mobility, body weight, incontinence and nutrition), and external factors (e.g. long trolley waits in accident and emergency departments or before admission following a long period collapsed on the floor, hard chairs, and immobilization with traction).