You can make use of lightening creams or ointments. Although these can also be effective, you will spend a lot of money on these products, and may also expose yourself to the side effects of the toxic chemicals they contain. So, it would probably be better to favor natural methods.
1- Baking soda:
Baking soda is very effective in cleaning the skin and reduces darkening in the elbows and knees. Take a tablespoon of baking soda and mix it with milk
Apply this paste on the knees and elbows and rub in a circular motion. Repeat the remedy once every two days. Repeat until you notice changes in the color.
2- Sugar and olive oil:
The sugar in this home remedy has exfoliating properties and olive oil will hydrate the skin. So mix equal amounts of olive oil and sugar to form a thick paste. Apply this mixture on the black knees and elbows.
Rub the skin using this mixture for about five minutes. Wash with mild soap and water.
3- Turmeric, honey and milk:
Turmeric has antiseptic properties and milk acts like bleach. As for honey, it hydrates dry skin and also has antiseptic properties. These natural properties combined in these ingredients will help get rid of black elbows and knees.
Mix turmeric with milk and honey to make a smooth paste. Apply to dark areas and leave it on for at least 20 minutes. Then rub the areas with your hands for 2 minutes, then rinse with warm water.
4- Lemon and honey:
Lemon juice has natural whitening properties and honey hydrates the skin and prevents darkening. Take the juice of a lemon and mix with a tablespoon of honey.
Apply the lemon and honey mixture to the affected areas and let the mixture act for at least 20 minutes. Repeat this tip at least three times a week for best results.
5- Chickpea and lemon flour:
Chickpea flour can cleanse dark areas of the skin and also provide gentle exfoliation. As lemon is a natural bleach, add a little lemon juice to chickpea flour to make it moist.
Apply the mixture and rub in a circular motion, allow it to dry completely and wash it off to get lighter skin.