Normally I find that creases in the neck, when the head is rotated, the armpits etc are best made less definite, but not completely removed. They are not natural focal points in an image, and when backed off are usually not noticed at all by most viewers.
IHP (inverted high pass) is a very effective and quick way of achieving this result if you are in a hurry, or want to spend your quality retouching time on the face rather than someone's armpit. Basically what it does, if you get the right setting, is to reduce the strength of the areas of light and shadow along either side of each individual crease while still leaving the actual crease intact. You need to play with the setting to get the optimum effect. I tend to be wary of using IHP, but this is a scenario in which it can save a great amount of valuable time, without making the retouch look artificial.