Thick, dry, blackened skin on the knees is a result of hyperpigmentation. A combination of dry skin, friction and accumulating dead skin cells result in a callous-like darkened area on your knees. This condition is embarrassing and irritating, but needn't be permanent. Although proper skin care and preventive measures help keep your skin smooth and moisturised, steps can be taken to restore your knees to a normal appearance and feel, allowing you to wear skirts and shorts without being embarrassed by the appearance of your knees.
Slice a lemon in half with a paring knife. Prop up your feet so the lemon juice won't drip completely off your knees during treatment. Rub the lemon halves on the black skin on your knees each morning and allow it to sit for 15 minutes to help naturally bleach and exfoliate the skin.
Squeeze lemon juice over a pumice stone and rub the skin on your knees in a circular motion to loosen dead skin cells. Rinse your knees off with water and dry with a clean towel. Apply a dry skin moisturiser to your knees. If you're heading out of the house, apply sunscreen to your knees to prevent discolouration from sun exposure.
Stir together 1/2 tsp lime juice and 1 tsp coconut oil in a bowl to make a skin-lightening moisturiser. Massage the lime and coconut oil mixture into the dark skin on your knees. Allow the moisturiser to absorb into the skin for 20 minutes.
Blot your knees with a clean absorbent towel to remove any remaining lime and coconut oil. Rub dry skin moisturiser into your knees to seal in moisture.
Repeat these steps daily to achieve desired skin condition. Maintain the appearance and feel of your knees by exfoliating and moisturising regularly. Mustard oil massaged into the knees helps to regenerate skin, leaving your knees looking healthy and feeling soft. These steps can be used for dry, darkened elbows, as well.