Wearing an ill-fitting bra can cause some discomfort and pain, but underwires themselves aren’t to blame for causing back pain. If you’re wearing a wired bra or even a non wired bra that’s the wrong size, this can cause some discomfort and even back pain. As any woman who wears a large bra size knows, having a bra that fits well and provides the support you need is crucial for avoiding the back and shoulder strain that can come with having large breasts.