Don't toss that white ball cap in the trash once it is dirty and stained. You may worry that washing your baseball hat will ruin it, but most of today's caps are made of durable material that can withstand being washed in the washing machine. Take care of your cap and keep it looking new with regular stain treating and washing.
Treat the stains on your hat. Use a pre-treater spray or stick and apply it to the stains on your cap. Pay careful attention to the brim of the hat which may have sweat stains. Rub the pre-treater in with a little cold water.
Stick your hat on a plastic cage that will help it hold its shape while it's in the washing machine. These are sold at most retailers and are inexpensive.
Put your cap into the washing machine with a mild detergent and cold water. If you're really nervous, use the gentle cycle. If the hat is severely stained, you can add a booster to the wash such as a little bit of borax or other stain remover.
Allow the hat to air dry. Never put a hat into the dryer. This could ruin it and cause it to lose its shape or shrink.