Fungal infection or Ring worm.. when occurs in groin, called as jock itch.. Usually fungal infection is common in moist areas of body like skin folds..It's mostly circular or round in appearance.. May be red or black in colour.. Treatment depending on the type and severity.. Avoid sharing clothes, towels and soap; sweating also increases it..As it has to be differentiated from eczema and infection, its a must to see and confirm the diagnosis for proper treatment..So, please send photos of the affected area for accurate diagnosis and treatment.

This description sounds like acanthosis nigricans. This is a condition where your skin​ folds like underarms, inner thighs or groin, neck and face becomes dark. It is either genetic or due to sedantry lifestyle and overweight. This can be treated. Please call me or contact me with photos using online consult option for proper diagnosis, treatment advice and prescription.