Welcome to HCM
We understand your concerns
I went through your problem description. I suggest you not to worry too much. Groin area is prone to excessive sweating
and thereby itching and skin rashes. The best way out of it is to keep it dry and clean. There are so many hygienic ways to keep yourself dry and clean.
The white patch
you are referring could be the mixture of sweat, dust, dead cells and other micro organisms. This is also common. If you are still in doubt, you can visit a physician instead of worrying yourself.
Hope this clears your doubts. Available for further clarifications.