They could be just a covering for one's body. Perhaps it is our skin that is the costume when we add make up and different color here and there.
One thought that may not crossed your mind. Is that each outfit we wear, and any make-up we use is a way to make a costume. When you take away all our covering we are more than all the same then with what we wear and what we do to our bodies. So in that, that is our costumes not these outfits we put on over it but what we do each day. In sense we are always in costume.