Whether it's due to weight loss, or simply as a natural result of ageing, at some point, we start to notice that the skin of the neck and face seems to have lost some of its elasticity and we're starting to sag a bit under the jaw line.
First of all, if you've lost a lot of weight, remember that your whole body is adjusting to its new shape, and skin, too, needs time to adapt; after a few months you'll probably find that it's 'settled' a bit and the sagging isn't so noticeable.
Apart from that, though, there is no easy solution, and once the signs start to appear, there isn't a great deal you can do about it. This, of course, is why those 'nip and tuck' operations are so popular. But whether it's because of financial considerations, or for whatever reason, not all of us want to resort to the surgeon's knife, so it's worth taking action before surgery becomes the only option.
The skin around your neck and jaw is delicate; it's a good idea, then, when you do your daily facial routines of cleansing and moisturising, to extend the process to include this area. Skin does lose elasticity with age, but well-moisturised and hydrated skin is always more adaptable and less likely to sag. You can try using a reducing cream or firming cream under the jaw, too as this can help to tighten the skin.
There are also exercises that can help to improve skin tone and combat sagging if performed regularly. Neck stretches will help to tone the muscles and improve circulation. Try making an exaggerated 'O' shape with the mouth, feeling how it stretches the skin. Do this ten times, holding the stretch for three to five seconds each time. Then do a similar series of exercises with the letter 'U', and end with another series with the letter 'X'. Each letter shape will use slightly different muscles, helping to keep them flexed and toned.