Double chin is a problem for a lot of people and is usually due to a local collection of fat between the skin and the underlying muscle. Weight loss in general may or may not get rid of it and the loss of jaw line definition associated with it can give an ageing effect.
Now there is an FDA and TGA approved injectable form of deoxycholic acid which breaks down and absorbs fat that can treat this problem. Deoxycholic acid is found in our bodies as a type of bile acid involved in breaking down fats and this has been synthetically reproduced to make this product.
Note: It always causes bruising and swelling which can be marked in the first week but does go completely. Some patients need a second treatment a month or so later and it can give a great contour in the right people. Best results are seen 2-3 months later. If the problem is really loose skin rather than fat, this treatment will not help.