Sleeping on your chest does not directly cause breasts to sag. Sagging of breasts, also known as breast ptosis, is caused by a variety of factors such as aging, pregnancy, breastfeeding, weight fluctuations, genetics, and other lifestyle factors such as smoking.
However, if you frequently sleep on your stomach, it may put pressure on your breasts, which over time could contribute to breast sagging. This pressure can stretch the ligaments that support the breasts, leading to decreased elasticity and increased sagging over time.
To prevent breast sagging, it's important to maintain a healthy lifestyle, maintain a stable weight, wear a well-fitting and supportive bra, and avoid smoking. If you prefer to sleep on your stomach, you can try using a soft pillow or a specially designed pillow to reduce pressure on your breasts while sleeping. It's also important to note that breast sagging is a natural part of the aging process, and some degree of sagging is normal and expected over time.