Getting rid of dark spots depends on the cause of the discoloration, but homemade remedies with lemon juice help diminish the dark spots over time. Lemon contains an active ingredient called L-ascorbic acid that promotes healing in the skin and hair. Many people use lemons and lemon juice as home remedies for a number of ailments including discoloration of the skin, according to Med-Health.net.
Med-Health.net not only notes that lemon has natural skin lightening properties but also mentions that lemon presents one of the most cost effective methods for lightening dark spots on the body. The nutrient L-ascorbic acid contains potent antioxidant properties that promote healing while cleansing the skin. Med-Health.net also notes that lemon juice helps speed up the lightening process for dark spots that eventually heal over time, such as those from mosquito bites.
Find Home Remedy also lists six other home remedies that effectively work to lighten dark spots on the knees. These include almonds, baking soda, oatmeal scrubs, olive oil, Vaseline and vitamin E oil as potential healers of dark spots, especially when these spots occur as a result of an accumulation of dead skin cells on the knees. The site also mentions that lemon has natural bleaching properties.