What Causes Itching On Legs And Black Spots On Body?

doctor , i am 28 yrs old, suffering from a itching in my both legs . after heavy itching on my legs, black spots began to develop and it spread to other parts of my body too. the spots are many, under the thigs , calf, wrist. At some places where the itching had occured, skin has become lose and has shrinked with a black spot. what could be the reason sir,is there any remedy