How Can Black Hard Callouses Be Treated?

i m 32 male 5 ft 5 inch and weight 55 kg suffring from crack on under toe and finger of leg and finger of hands getting hard (palm side) and forming hard and dry also its colour getting black and hard i consulted doctor since three month got ointment of salicylic acid combination and one tablet cetrizine daily to take.it is curing but another place it is buzing same problem.please suggest me remdies.