Check the care label first
Spot-test any cleaner on a hidden area
Mix cool water with a small amount of mild detergent
Dip a soft cloth or toothbrush into the solution
Gently scrub the sweat-stained areas
Use a cloth dampened with clean water to wipe away soap
For stubborn stains, apply a paste of baking soda and water
Let the paste sit for 15 to 30 minutes
Gently brush the area with a soft toothbrush
Rinse with a clean damp cloth
Air-dry the hat on a towel or hat form
Keep the hat away from direct heat and sunlight
Repeat if needed
Avoid bleach unless the care label says it is safe
Avoid soaking structured hats for too long