Does not wearing a bra cause sagging?

Not wearing a bra can contribute to breast sagging because bouncing and movement can loosen ligaments over time, contributing to ptosis.

While some sagging is genetic, a portion of ptosis can occur from excessive bounce and stretch. Over time, stretching of the skin can lengthen Cooper’s ligaments (the fibers that anchor breasts to the chest wall). When those ligaments lose their elasticity, you’re left with a sagging effect. 

This is especially common with heavier breasts. To combat this, be sure to wear a supportive sports bra during exercise and a supportive bra t-shirt or full coverage bra during daily activities.