They're made from parts of certain plants like leaves, herbs, barks, and rinds. Makers use different methods to concentrate them into oils. You may add them to vegetable oils, creams, or bath gels. Or you might smell them, rub them on your skin, or put them in your bath. Some research shows that they can be helpful, if you know how to use them the right way. Always check the label and ask your doctor if you’re not sure if they’re OK for you to use.