Dark Marks Caused by Bra Straps

If your breasts are bulging over the top or sides of your bra, or even from underneath, your bra is not the right size. These issues, along with strap marks, indicate that your cup size is too small. In addition, if the band of your bra is riding up above your shoulder blades, it is another indicator that your bra is too small.

According to Barenecessities.com, the support comes from the bra's band around your chest, not from the straps. If your straps are pulled too tightly, this is going to cause the dark marks in your skin. Furthermore, if the band on your bra is too big, the straps will end up carrying the load, which puts pressure on your shoulders and your back and will cause indentations.