Hi Katie,
After double chin treatment it does not cause loose skin. This was a actually a question that I asked at the launch of the product in Sydney earlier this year!
After treatment there is some swelling and inflammation under the chin in the areas that have been injected. This inflammation sets up a cascade of events which can cause firming/fibrosis of the area so, rather than leaving loose skin, the area can be firmer and tighter.
Many thanks
Dr Jonathan Brown
Cityskin