Hello. Thank you for writing to us at healthcaremagic
Judging from the description and the distribution of the skin involvement, I can keep a possibility of Tinea (
fungal infection). If it is Itchy too, that certainly would go in favour of Tinea.
A fungal infection classically involves body folds like groin, sub-mammary area and inter-mammary area.
Darkening is likely due to post-inflammatory
hyperpigmentation associated with the infection.
You may apply an OTC antifungal e.g
clotrimazole 1% cream, twice daily. However, oral antifungals e.g
fluconazole or terbinafine may also be added in addition to topical antifungals. Oral antifungals are prescription drugs.
I would suggest that you seek an appointment with a
dermatologist for a confirmatory diagnosis. A fungal infection can be easily diagnosed by visual inspection. KOH examination is also confirmatory of a fungal infection.
Regards