Lemon juice contains citric acid which is a natural bleaching agent. Therefore, applying lemon juice to elbows can help to lighten the skin. To use: Cut a large lemon in half. Squeeze out some of the juice from both halves so that you have two hollow halves or "cups". Rub each lemon cup on your elbows. You can rub away any excess pulp, but don't wash your elbows for about 3 hours. This gives the lemon juice time to sink in. Wash off the lemon juice with some warm water. As lemon juice can be drying, you should moisturize the area with petroleum jelly. Repeat this everyday until the dark skin begins to fade. You should see a significant difference within a couple of weeks.