Essential oils aren’t supposed to be applied directly to the skin undiluted because they can cause rashes, burns, and more dangerous side-effects. That’s why carrier oils are so important — they carry the oils safely so that you can use them topically. A carrier oil is derived from the fatty portion of a plant, usually from seeds, nuts, or kernels. Each one has its own therapeutic properties that can enhance the benefits of the essential oils that you dilute in them.