This could be due to extreme dryness, friction, eczema
, acanthosis nigricans
. To make a definite diagnosis of your condition, you need to consult a dermatologist
. In the meanwhile, use very mild glycerine based or oatmeal based soap to wash hands. Use Xerina cream to moisturise hands at least twice to thrice in a day. Also use topisal 6% ointment over dry and dark areas preferably under occlusion in night. Under occlusion means after applying the medicine wrap a plastic sheet over it as this aids
in better absorption of medicine. Try the above mentioned treatment for few weeks. It will help you out. Take care.