Near-Infrared cameras can see through many thin fabrics and some other materials. If you wear a good enough mask, it shouldn't be a concern. But most cheap Halloween costumes are made of the exact materials that can be seen through, which is a whole other concern. I had to demonstrate how easy it is to see through some clothes with the right (easily accessible) equipment for my mom to force my little siblings to wear full proper clothing under Halloween costumes. (I'm much older than the youngest kids in my family.