It can be improved...it's due to frictional dermatits...Undergo glutathione therapy.. otherwise few creams also available...for detailed prescription do direct online consultation by sending photos.

U could b suffering from acanthosis Nigricans. It's a condition characterized with pigmentation of the inner thighs and also the underarms. Weight gain is the most common causative factor  weight loss with adequate medication will help reduce it. The circular lesions forming could b a fungal infection. corroborate with pictures for a better understanding.  Consult a Dermatologist for the same.