I Have A Very Dark Patch Around The Corners Of

I have a very dark patch around the corners of my mouth and has turned worse from last couple of years. I used alograce cream and took vitamin C and tried few homemade remedies but nothing helped. Also, I'm suffering from hyperthyroidism for like last 4 years and take neomercazole tables ever since it was diagnosed. Please tell a permanent solution to get away with this problem.