Good evening mam, my dermatologist suggested me to use tretinoin 0.025% for acne marks and dark spot and for also open pores I started applying alternate days pea size amount on first day I didn't any irritation or redness it was normal for me but I was not using regularly it has been 1 to 2 week of using but suddenly I noticed my has become dark I stopped using it mam can skin will become back to its regular color .this skin darking will go away by itself or not.