Young Indian Girl With Pigtail And The Red Bandanna

Wildland firefighters wear them over the mouth and nose to lessen inhalation of dust and fumes.
Dancers and other athletes wear them during practice as a simple way of keeping hair and sweat out of their faces, or as part of their costume/uniform.
Soldiers wear them to keep their own sweat and blood out of their eyes.
Kitchen staff may wear them to keep hair from falling into the food that they prepare.