There are a number of ways to tighten skin, but skin can only be retightened to a certain point, after which the dreaded 'tummy tuck' surgery must be undertaken.
The following are ways to tighten sagging stomach skin:
Cocoa Butter Firming Moisturizes Drinking lots of water
Other options that are less off the shelf are:
Arasys - electro-stimulation of the abdominal muscles and blood vessel
Laser therapy - this is used to make your body generate collagen, which will tighten up your skin
Collagen Injections
Tummy Tuck - a surgical procedure where they remove a segment of loose skin. Remember, ALL platic surgery is serious,and more invasive than most types of essential medical procedures.