hi,circular dry patches on the legs are due to nummular eczema
.it is due to dryness of the skin.these patches turn dark after repeated itching.
avoid repeated washing of the legs ,washing the clothes.use a good moisteriser like elovera imf twice daily. apply dipsalic ointment in the first week and momate in the second week to decrease both the dryness and darkness.
use moisteriser even after complete treatment to decrease the recurrences