How to Whiten Dark Elbows, Underarms And Knee Easily At Home This is 100% natural treatment that can give you effective results within a month 1. Squeeze juice of lemon and apply it on your elbows, knees and underarms. Leave it for 15 minutes and then wash it off,. Do it on daily basis to see results in few weeks 2. Take 2 tbsp of baking …