REASON

If tightening the strap is not working, the problem could be that your cup size is too big - You're not filling out the top of your cup (probably because you have shallow upper breast fullness and this is causing your straps to slide down your shoulders.



You’re using bra extenders which move the bra strap placement closer to your shoulders’ edges.



When putting on your bra, you are not making certain your bra's back is pulled down and under your shoulder blades.



Your band may not be tight enough or a size too large and the straps in the back are thus too close to the edge of your shoulders.



Your bra style could be the problem -wide-set straps are very popular, but if you have small or sloping shoulders, this style is not for you.



Your bra straps are attached to a ring either in front or back. This ring allows your straps to swivel and thus contribute to them falling off your shoulders.



You were born with narrow or sloping shoulders.