It seems incomprehensible that something as prosaic-sounding as a bedsore should have finally killed Christopher Reeve. But he has been at great risk from overwhelming infections since he was first paralysed in 1995.

Anyone who sits or lies in one position for a long time can develop a bedsore, also known as a pressure sore. Wheelchair users are particularly susceptible and Reeve's carers would have taken great care to ensure that he was turned and moved frequently to try to prevent sores developing. He would also have sat or slept on fleeces and other cushioning surfaces to protect his skin from the pressure of his weight. Poor blood supply to the skin with diseases such as diabetes can also make you more prone to sores.

Pressure sores develop on bony parts of the body that don't have much fat to cushion them. The body's weight damages the skin in areas such as the heels and the base of the spine. The blood vessels in tissue under the skin get squashed and damaged. Without a decent blood supply, sores develop, fail to heal and get bigger. If not treated, the sores can get progressively deeper, extending down through the skin layers, fat, muscle and, eventually, to the bone.

Most bedsores are successfully treated by relieving the pressure, cleaning and dressing the sore and improving nutrition. But there is always a risk of infection from bacteria that normally live on our skin. Any infection is treated with antibiotics, which are given orally or intravenously. But if a person is malnourished, has a poor immune system or is generally debilitated, the infection can put a huge strain on the body as bacteria multiply in the sore and flood into the bloodstream.

Reeve's internal organs would have been assaulted by a flood of damaging bacteria, the strain on his body possibly causing the heart attack from which he apparently died. The fact that he has been so vulnerable for the past nine years make his passing no less tragic.