I Have A Black Mark On The Penis Forehead Around

I have a black mark on the penis forehead around the hole. It's not like that in my childhood but later I didn't observe when it became like this. I just googled about my problem and found that it common and no need to worry until the size. Now the size of the mark is almost 50% of the area. I'm not sure if its safe or not. Anyways I don't want it to be like that. Please help me with a good solution. I stay at Secunderabad. Ready to consult personally.