hi..thanks for you query.
There are several possibilities that can happen in the above scenario.You may be getting Candidial intertrigo
due to maceration of skin .There is a possibility of a contact dermatitis
due to soap/ any other material coming in contact with the area.Any tight and occlusive underwear or trousers /clothing may cause the same due to friction.
To avoid the same , try out the following:
-Use loose fitted clothes always.In case you sweat profusely, you should be able to change inner wear -3 times a day.
- Avoid soaps in the same area
- Always keep it dry. You can put ant anti-fungal powder after you take bath etc.
If they still persist, please visit a dermatologist
to get an opinion on the same.
Hope this is helpful.Take care!