Cerebrospinal fluid is also called CSF. Like other cells in the body, brain cells produce waste products. CSF cleans the brain by washing away the waste products that are made every day by brain cells. Your brain is always being cleaned by CSF, but it is cleaned more when you sleep than when you're awake. That's one of the many cool and important things that your body does while you sleep! CSF surrounds and washes the brain to make sure that all of the chemicals that should there are there, and to make sure the chemicals that should not be there are gone. CSF also protects the brain by absorbing shock-- it prevents the brain from being damaged if the head is hit or suddenly moves quickly.