If bra straps keep falling down, it could be due poor bra fit. However, it could also be because the bra style does not work with that particular body type.
Usually, slipping straps occurs because of a badly fitting bra. There are a number of fit issues that can cause straps to fall down. The most common of these is loose straps. This is usually a very easy issue to fix. If straps are slipping, try tightening them.
A cup size that is too large can also make straps fall down. If there are any gaps at the top of the cup, this creates a lack of support, which can make straps slip. Women can solve the problem by going down a cup size or creating more lift in the bra cup.
Large bra bands can make straps slip. This is because the straps sit further apart, causing the spacing to be too large for the body. Another common sign of an oversized band is the back of the bra riding up. If this is a frequent problem but the cups of the bra still fit, choose a bra one band size down and one cup size up. That way, the cup volume is the same, but the band size is tighter. In the same vein, bra extenders can cause strap slippage, as they create more spacing between the straps. If the band of a bra is too snug, consider buying a new bra with a larger band and a smaller cup size.
Sometimes, straps slip because the bra is the wrong style. Women who have narrow shoulders should choose styles with straps that sit closer together. URacer back and leotard back styles work better for women with narrow shoulders.