breast asymmetry, used to be widely believed to happened because of the positing of the heart but we now know its unrelated and that was a myth, it's hormonal fluctuations or weight changes most of the time when its temporary but can also just be the general skeleton structure or posture development during puberty.
However it affects most women (like 80 to 90%) to some degree, in the shape or size of the breast, some its very visible some not as much but most women try to hide it for pics or just straight up edit it. irl it's quite easy to see and feel good idea to not comment on it tho lol