Washing with a papaya-based soap can help you lighten the area, but you can also prepare a mask with this fruit. Just crush some papaya and apply it to the affected area. Then comes the tricky part: let it sit for 30 minutes to give the fruit time to act (yes, this part isn't really comfortable...), then finally rinse. Repeat this a couple times a week and you'll soon notice a difference.
A mixture of lemon and a little yogurt can also be effective. Apply the mixture to the dark area, let it sit for 20 minutes, then rinse thoroughly. Finish by applying a moisturizer. Be careful not to expose this area to the sun immediately after this procedure, and don't do this right after hair removal.
Make a paste out of ground almonds and a few drops of almond oil. Apply it to the area, let it sit, and then before removing, take a moment to gently exfoliate the skin.