Welcome to HCM.
You are suffering from Intertrigo- inflammation of body folds characterized by redness
and irritation over the affected area. It most commonly affects our crural folds ( Fold between abdomen, thigh and scrotum/ Labia).
Now the very first thing is you should not wear jeans for long term, rather should wear some loose pants made of cotton clothe. The undergarments are to be changed twice in day. Avoid excessive exposure to heat and humidity. Do not scratch the area of itching. At night time give warm water compresses to soothen your skin. I day time you can use Dusting powders to reduce sweating.
For the Dark areas of your thighs, Kindly reduce your weight. Till the time you are not reducing the weight, the continuous friction and trauma will cause increase in pigmentation. You can apply Hydroquinone
containing creams or azelaic acid cream or glycolic acid
cream to the affected areas under dermatological guidance.
Hope this information will help you.
With best health wishes,
Dr Sanjay K Kanodia