Apart from these methods, you can prevent the darkening of your elbow and knee skin by not sitting on your knees and by not putting weight on your elbows. Doing this can wear them out more quickly, and prevent proper flow of blood through them, thus making them darker. So, use these tips to get rid of dark elbows and knees.
Do you feel embarrassed due to dark knees and elbows? Do you refuse to wear skirts or shorts or sleeveless tops because of the dark colour of your knees and elbows? Yes? Here’s something to make you feel better – darkened elbows and knees is a common problem, which can be handled quite easily and quickly.
Most commonly, the skin of elbows and knees darkens because of dead skin cells on them. The skin is thicker in these areas, and compared with other areas, is more prone to the loss of moisture. In addition, people tend to lean over them, thus making the skin rougher, coarser and darker. So, if you want to keep your elbows and knees soft and fair, you should not neglect them during your skin moisturizing and body care routine. 
With a little care and extra time, you can remove dead skin cells from your elbows and knees, and bring them back to their former fair and soft self. Here are a few tips:
Scrub: Scrubbing the elbows and knees will remove flaky, dry skin cells from areas that get trapped in their creases. Apply some exfoliating shower gel on a washcloth or loofah, and scrub for a few minutes to remove dead skin cells in the areas. Make sure you do not scrub too frequently or too hard, as extra skin cells may be produced and the areas may become even darker. It is best to scrub only once a week, and that too very gently. Have patience, and you will notice the difference within a month or so.
Moisturize: Dry skin appears darker, so do not forget to moisturize these areas. Moisturize after every bath or shower, as warm water may remove natural oils from your skin, thus making it harder and darker. Moisturize before going to bed every night, and also every morning before going out for work.
Avoid sun exposure: Prolonged exposure to direct sunlight may damage your skin, and make your elbows and knees look darker. So, avoid going out in the sun, and if necessary, do not forget to wear sunscreen. Most people apply sunscreen on their face only, but you should not ignore your hands and legs too. Ultraviolet rays are equally harmful on rainy or cloudy days. So, you should apply it everyday, no matter what season and weather it is. 
. Skin - abnormally dark or light: MedlinePlus Medical Encyclopedia. 2016. Skin - abnormally dark or light: MedlinePlus Medical Encyclopedia. [ONLINE] Available at: https://www.nlm.nih.gov/medlineplus/ency/article/003242.htm. [Accessed 19 January 2016].
. Sun Exposure: MedlinePlus. 2016. Sun Exposure: MedlinePlus. [ONLINE] Available at:
https://www.nlm.nih.gov/medlineplus/sunexposure.html. [Accessed 19 January 2016].