So I have been bra free for the past 3 days just to breath a little bit, and I have noticed these lines under both my boobs (more on my left one shown in the picture)

What could it show?

Ps. I’m not worried, just curious if it means breast growth (😊) or if it is formed there because of another reason. It is not painful at all, I literally feel nothing. Above that line there is a bit of volume coming outward but not too much. What do you think?

(I’m B cup)