Take a toothbrush and scrub the sweaty parts of the hat with some shampoo, then wash the hat. most hats will keep their shape just fine in the washer and dryer.....or air dry. shampoo is made to break down body oils. you can also use this tip for ring-around-the-collar.
You can also stop sweat stains before they happen. I use a product called Hat Saver that you spray on the outside of your new hat and you never get sweat stains to clean. I then just wash the headband on the inside of the hat if it starts to smell or gets real dirty. You can buy it at hatsaver.com.
In addition to sprays and washing, you can also protect your hat with a wicking hat liner, like the CrownWear Head Liner. The keep sweat out of your eyes and filter out the dirt, salt and oils in your sweat to prevent stains and odors and extend the life of your hat.
If the cap is at least hand washable, dish detergent or other soaps designed to attack grease, oils or fats generally work pretty well. Try a dish detergent that has no color and no scent to it if you're worried about not being able to wash it out completely. Lemon juice, vinegar, and other mild acids are good too, but again, try to stick with clearer vinegars (white wine, rice or other white vinegars) if you can't throw the cap in the washing machine and are washing by hand.
Try washing it along with dark clothes in the waher. If not, try using baking soda and scrubbing with a sponge or dish brush. Rinse A LOT. Anyhow, how did yu get soot in your Baseball cap?
wash it with warm water and soap then hag it to dry
You get rid of oil stains by using oxce clean
Perspiration is salty because of the excess salt from the body that are secreted as waste. Perspiration is the body's mechanism to get rid of excesses in addition to water.
scrub it
Soda!
bleach is the most effective way to get rid of stains it removes all the dirt and cleares out the stain.
your mom
peroxyed
You can either soak your stained clothing in the bleaching agents or detergents to get rid of the stains.
I do believe perspiration (a.k.a. sweat) is caused because the body is trying to get rid of the toxic gases and other bad things inside the body. I do hope this helps.
Rub it clean with arsenic
Try a little bit of Golden Syrup (see 'How do you remove grass stains?)
Try Resolve carpet cleaner, that worked to get most all of the stains out of my carpet when i moved.