It totally depends on what oil or combination of oils you're using. Essential oils can help your body heal physically from topical things like cuts, rashes and pimples to deeper ailments like muscle aches, menstrual cramps, and poor circulation. They can help when you're sick from headaches to colds to the flu. They can help you relax and reduce stress, or help concentration, or help wake you up out of a bad mood. Pretty much any acute ailment you can think of, one or more essential oils can help. Even chronic ailments (along with, not in place of, modern medicine) can be helped with essential oils.