There's also some evidence a bare knuckle blow to the head may do less damage than a boxing or MMA gloved strike because the surface area is smaller, some believe gloves may add to the risk of a concussion aswell.
Not only that but also fighters don't hit as hard due to fear of breaking their own hand. With gloves fighters can almost punch as hard as possibly can without too much fear, however with bare knuckle the chances of damage increase dramatically.
RE: Bare Knuckle Boxing Returns to the US