Thanks for posting your query.
Dark skin on inner thighs could be as a sequel to a fungal infection
It could also be due to other reasons like friction, allergy etc.
The following measures would be helpful:
Keep the area dry and clean.
Wear cotton clothes.
Apply Vitamin E
cream like Sofderm or Hovite AO thrice daily on the affected areas.
Diet and exercise if you are overweight
, and this is causing friction between the thighs.
like applying cocoa butter sometimes helps.