Hi Dr, 15 days ago. I got dryness on the left side of my mouth and it was very itchy and flaky, and then I got a pimple in the same area, so I applied a drop of retinoid on it to settle the pimple. After which I started to notice the area becoming darker until it had become very dark that I had to consult a dermatologist and she diagnosed me with post retinoid hyper pigmentation. I want to know how much time will it take for this mark to fade away. it is really bothering me a lot. Do you have any other diagnosis for this respected doctor? Please help me.