Add 6- 12 drops of essential oil to a warm bath with a pound of salt and soak for 15-20 minutes. Do not use oils that are caustic or sensitizing. The pores of the skin dilate due to the hot water so oils that are not usually sensitizing can become sensitizing in this application (ex: Tea Tree, Clementine, Elemi, etc.). If you start to feel a burning sensation it is best to get out of the bath.
Salt Bath is one of the many methods of using essential oils.