As we gain weight our skin stretches just like a spring does when pulled from both sides. At a certain point, the elasticity (the ability of skin to spring back), is damaged. If the weight gain continues, the stretching / pulling continues and finally all elasticity is gone. At this point, depending on the speed of weight gain, the the skin may start showing cracks ("Stretch Marks") - these are permanent through and through scar filled cracks in the skin which can never be erased. When all the weight is lost, the damaged skin does not spring back and just hangs there. The BEST way to tighten such loose skin is to remove as much of it surgically (Tummy Tuck, Buttock Lift, Lower Body Lift, Breast Lift and Face and Neck Lift). If a non surgical tightening is opted for, the success of a non-surgical method will depend how much of the skin is loose, where on the body it is located, how thick it is etc. Nice responses can be seen with IPL (intense pulse light) devices. The most promising appears to be Sciton's BBL with the SkinTyte feature. Several painless sessions are required and in many people the results are quite pleasing. Look it up on You Tube. Dr. P. Aldea