My son is hitting his head!

Hi everyone, my toddler (he’s 20 months) is always hitting his head! Whether it be him getting told no or getting into trouble or just playing.. he’s always running and happens to run into a door, a wall or him falling and hitting his head. He cry’s sometimes but most of the time he doesn’t. What can I do, help me please!! I’m just scared that he might really hurt himself one day!