A bra, short for brassiere or brassière, is a form-fitting undergarment designed to support or cover the wearer's breasts. Bras are designed for a variety of purposes, including enhancing a woman's breast size, creating cleavage or for other aesthetic, fashion or more practical considerations. Swimsuits, camisoles, and backless dresses may have built-in breast support with supportive bra cups. Nursing bras are designed to facilitate breastfeeding. Some women have a medical and surgical need for brassieres, but most women wear them for fashion or cultural reasons. There is no evidence that bras really prevent breasts from sagging.