Young Indian Girl With Pigtail And The Red Bandanna

Outdoor workers, such as farmers and cowboys, wear them around the neck to wipe the sweat off their faces and keep dust out of their collars.
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.