When used in a bath, the magnesium sulfate – Epsom salt is absorbed by the skin. This can cause the skin to soften and some of the substances that the skin absorbs day-to-day to be drawn out.
Occasional use of Epsom salts (especially on the feet) does not seem to be harmful. Many people swear by Epsom salts, though there doesn’t seem to be many scientific references to its use. There are a few cautions of using Epsom salts, however, and they are mostly for people with dry skin.