Get Rid of Armpit Stains FOR GOOD! Make Your Own Deodorant | One Good Thing by Jillee. 1/4 cup cornstarch, 1/4 cup baking soda, 10 drops of tea tree oil. mix well and apply to armpits.....OR: 2-3 Tbles coconut oil, 1/8 cup baking soda, 1/8 cup cornstarch. (warm oil then mix the other ingredients to thick paste & apply).