All women should wear sports bras when they run. The Cooper’s Ligaments which support the breasts can be permanently stretched and damaged if the breasts are not properly supported during exercise. This leads to droopy breasts, and cannot be reversed. A good sports bra provides support for your breasts to prevent them from bouncing while you run. In addition, surveys show that half of women who exercise suffer from breast pain, and this is an important reason why they give up.
Sports bras essentially work in two, different (not necessarily mutually exclusive ways):
they compress your breasts against your body, to reduce the bounce; and/or
they individually cup each breast, and so provide each breast with support.
It is often said that women with large cup sizes prefer sports bras that support each breast individually; while women with small cup sizes prefer sports bras that simply compress the breasts. This preference is not universal, however – and was not borne out at all in my (admittedly unscientific) survey of women runners who I asked about this.
