Why skin stays loose after weight loss
Sagging skin after weight loss has a simple cause: the skin was stretched for a long time. It owes its firmness mainly to two protein fibres in the dermis, the middle layer of the skin – collagen, which provides strength, and elastin, which brings the skin back into shape after it has been stretched. If body weight is high for years, these fibres are permanently overstretched and partly damaged. Visible signs of this include stretch marks, for example.
When weight falls, the tissue lacks the volume that used to fill it. Part of the skin contracts. Whatever was stretched beyond its limit remains as loose skin – after very major weight loss also as skin folds or flaps of skin hanging over the abdomen, upper arms or thighs. This is not a sign that something went wrong with the weight loss, but a common consequence of a great success.