This is dermatitis most probably.

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 more photos of the affected area by direct online consultation for accurate diagnosis and treatment.

Need more history for proper diagnosis. Please stop Dettol, powder makes the skin dryer and causes more itching and deodrant contains alcohol which is worsen itching. Please contact me using online consult option for proper examination diagnosis and treatment