Clean the leather of any substances or light stains. Use a damp, warm rag and wipe back and forth on the stain.
Put on rubber gloves. Any time you're working with bleach or bleaching chemicals, you should wear hand protection.
Mix a specialty bleaching product or oxalic acid. Different products should come with directions, but for most bleach products you'll need to mix together one ounce of bleach with a pint of water. The oxalic acid should be mixed one teaspoon to a pint of water.
Wet your rag in the mixed solution. Rub down the garment's stains several times. Look closely to see if the stains begin to dissolve.
Wash the leather in a washing machine. Set the machine to cool water and a light cycle. This should be used only if you have a large, stubborn stain or wish to lighten the color of the leather.
Allow the leather to air dry. Never put leather in a drying machine because of the possibility of shrinking it.