I have seen women with necks and underarms darkening because of pregnancy. I know of someone who tried everything to lighten her underarms because she really hated looking in the mirror and wearing sleeveless shirts. But all her efforts were to no avail. Everything just went away after she had given birth.
Another concern of women aside from facial acne is neck acne. In www.neckacne.net I saw that they really have a different remedy for neck acne. And it should be because the skin on the face and the neck are different. So it should follow that the treatment for skin problems in different areas should also be different.
There are many kinds of neck acne treatment. But I know that sodium ascorbate works well for acne. I have heard of anecdotal stories that say direct application of sodium ascorbate heals pimples. I am not sure how true this is but it is worth a try.