Collagen or fat injections are used to plump up creased, furrowed, or sunken facial skin and/or add fullness to the lips and backs of hands. The procedure works best on thin, dry, light-colored skin and lasts 15 minutes to more than 1 hour per session depending upon the number of areas treated. Local anesthesia is used for both of these outpatient procedures. Side effects include a temporary stinging, throbbing, or burning sensation, faint redness, swelling, and excess fullness. The risks for collagen include allergic reactions such as rash, hives, swelling, or flu-like symptoms and possible triggering of connective-tissue or autoimmune diseases. Risks for both procedures include contour irregularities and infection. The duration of results is variable, lasting a few months to 1 year.