What can i do/use to tighten loose skin?

Loose skin: There are multiple options for treatment of loose skin. It mainly depends on the location that you are asking about. Often times it requires surgical excision and redraping of soft tissue.

Depends: Large amount of loose skin will require some form of tightening procedure. Tummy tuck for the abdomen, arm lift, thigh lift, etc...

Skin tightening : There are a variety of ways to tighten skin. For facial skin laxity, one can thermally damage the skin with a laser and achieve some skin tightening. A chemical peel can also do the same thing. For more substantial skin laxity of the face, breast or body - skin can be directly excised (face lift, breast lift, tummy tuck etc).

Depends: Significantly loose skin needs to be surgically tightened. Diet, exercise and time will not improve loose skin. There are several non-invasive options (zerona, vasershape, etc... ), but their results are not very impressive.