What Is the Cause of Decubitus Ulcers

What is the cause of decubitus ulcers?

A) The skin is infected with mites that itch, and the scratching causes ulcers.
B) Pressure on bony projections for a prolonged period of time cuts off the blood supply to an area of skin and an ulcer forms.
C) The cause is a tumor that starts in the lower layers of the skin and opens up to the surface causing a decubitus ulcer.
D) An allergenic agent irritates the skin and the decubitus ulcer is formed.
E) A caustic chemical such as an acid gets on the skin and causes the ulcer.