Don't know if this is the correct place to post this, but what is the best exercise for getting rid of a double chin? I know losing weight will definitely help, but are there exercises to help tighten up under the chin?
The 'double' chin is, as you suggest, deposition of body fat. You can't 'tighten up' fat tissue, only the underlying muscle, which won't show until the bodyfat levels are reduced.
There isn't a lot of muscle to work with through the chin. Try this. Isometrically contract the biceps of an arm. Place the opposing hand on the tigthening biceps. You can feel it, right? That's because there's some good muscle mass to work with.
Now, place your hand under your chin and see if you can tigthen anything in there, without contorting your face. Isometrically pretty challenging. You could use resistance by placing your fingertips under your chin and, holding your head stable, try to open your mouth which would activate the pulling muscles under the chin. You can feel that under your fingertips.
Activiating muscle is really quite simple. All muscles pull. If you want to exercise an area, get it into its most challenging pull position. The other way they work is to resist against the drop of gravity, where the muscle is contracting while at the same time lengthening (think of what your quads are doing as you lower into a squat).
I elaborate here just to make a point about muscle workload. To recap, you can challenge the muscle, but the body composition has to be such that it will show.
Thanks for your post!