Answer the following question given this paragraph: 

The mildest and most common type of brain injury is a concussion . This is a bruise on the surface of the brain. It may cause temporary problems such as headache, drowsiness, and confusion. Most concussions in young people occur when they are playing sports, especially contact sports like football. Other sports, like soccer, boxing, baseball, lacrosse, skateboarding, and hockey can also result in concussions. A concussion normally heals on its own in a few days.


Q: What is the mildest type of brain injury?


A:
concussion