Friends of ours have a daughter who was born with dwarfism. She could not crawl because her head was too large, arms too short. Typical of dwarfs, she adopted the "snow plow" manner of getting around, scooting on her forhead, pushing with her feet. Her forehead developed scabby skin, then a tough callous. After she learned to walk, her forehead returned to normal. It took a few months.
Also, my grandson took a bad fall a couple of years ago, major face-plant on blacktop. It took off large patches of skin, which scabbed and then turned pink. It looks completely normal now, except for a couple of spots where his cheek and forehead contain tiny specks of rock.