Bra straps adjusted too tight can cause soreness and leave tracks in your shoulders especially if the straps are too thin and your breasts are heavy. In extreme cases this simple strap problem can lead to headaches.
Bruising from tight straps
It could be caused by a band problem where the bra band could be too loose and not fit as snug as it ought to be; pulling on the straps so women compensate for the missing support by tightening the straps which digs as heavy breasts pull down on the straps seeking support which digs even more into the shoulders and deepen those tracks.
Take note ladies, spaghetti thin straps are not for the busty belle, if you must do thin straps, support the shoulders with these silicone cushion pads.
Silicone cushion pad