Mask, Disguise
A person who puts on a mask identifies with it; it is clear when observing children, indigenous people, and the double lives of superheroes that with the mask, they become someone else, something other. – One has the "right" to be a hero, a villain, or a monster, with the adequate mask.
This is what makes the mask frightening; when we encounter someone with a mask, we do not know what we are confronting. The person's true self is hidden, they lack a persona, and relational possibilities. This is probably why so many monsters in horror films wear masks.
When one puts on a mask, one receive protection from the surroundings. Psychologically, one does not need to be oneself, but there are also practical protections with masks – doctors, divers, firefighters, etc., wear masks.