Why Ghosts Wear White Sheets

There was one time I actually went trick-or-treating as a ghost wearing a bed sheet with two eye holes. Just once. I learned that it's impossible to keep the eye holes in the right place when you're walking, or doing anything. I guess that's why Charlie Brown had multiple eye holes cut into his sheet. When my kid wanted to be a ghost, I insisted on using a white bathrobe with a (non-pointy)  hood and plenty of white face paint. She changed that to a black robe with white face paint and was much scarier. 

But why are ghosts depicted as being covered in a white sheet? The art that makes them look like that goes back further than the trick-or-treat costume. Even today, when very few kids want to be a ghost for Halloween, we hang up balloons with white fabric over them to decorate our porches, because that says "ghosts" to us. Dr. Emily Zarka of Monstrum explains why.