To maintain a healthy tool, the penis needs to have erections regularly. Without regular erections, penile tissue can become less elastic and shrink, up to 1-2 centimeters. However, the brain has an “automatic penis maintenance” function. Brain impulses cause erections during REM sleep. For some men who are physically unable to have an erection, due to nerve trauma or blood vessel damage, they can use a device like a vacuum pump that causes the penis to swell with blood.