iphone 6s screen black dots

One day I woke up and I am seeing a strange black line o the screen of my iPhone. The screen is responsive though. (100% works ). It seems to be growing in size horizontally. I wanted to know if anyone had this problem before or can recognize this. Hopefully I dont have to change the screen of my phone for any reason.

When I take screen shots it comes proper ie no photo of the damage is shown. I have no idea how this happened though. It seems to be growing though and so that would explain it as liquid seepage.