Coconut oil is another good option to get rid of dark underarms. Coconut oil contains vitamin E that can help lighten the underarms. At the same time, it will also work as an effective natural deodorant. Massage the dark underarms with coconut oil. Leave it on for 10 to 15 minutes. Wash it off with mild soap and lukewarm water. Repeat two or three times daily until you achieve the desired results.