Our skin is the largest human organ. It acts as the body's outermost protective layer and comprises collagen and elastin, proteins responsible for the skin's strength and elasticity.
Over time and with increasing weight, these protein fibers tend to become weak, so much so that they are unable to retract to their original state when significant weight loss occurs.
In addition to losing a lot of weight in a short time, aging, smoking, sun exposure, and lack of hydration are some other primary factors that can cause your skin to sag.