I have the same on my underarm and I notice that my mum have it on both arm when I was growing up, I only have it on one underarm, It was when I had my first child that I noticed it there and I thought it will go away after I stop breast feeding, but I still have it, I consulted my
doctor about it and he said it is
a breast tissue
that some women have it and it is
not dangerous. He said they can do a surgery for me, they can remove it and after two days I will feel better.