Age and weight loss are the two biggest contributors to loss of volume in the skin. Over time, your skin produces less collagen and elastin.
These are two essential proteins in your skin that are responsible for the structure of your skin. This is what gives younger skin a youthful “bounce.” When your body makes less collagen and elastin, your skin is more likely to sag in certain areas and can become crepey and develop skin laxity.
When you lose weight quickly, your skin may not keep up with the amount of fat loss at the same time, causing sagging skin.