Any number of mishaps, such as a car crash, contact sports, or bump to the head, can cause a concussion. During impact, the brain slides and bumps into the inside of the skull. This can bruise the brain and tear nerve tissue. Concussions also shake up the balance of chemicals in the brain, harming nerve cell function and triggering inflammation. While the brain usually heals on its own, getting multiple concussions may lead to long-lasting damage.