If applied to the skin undiluted, essential oils, CO2s and other concentrated aromatics can cause severe irritation, sensitization, redness or burning or other reactions. Carrier oils are used to dilute essential and other oils prior to topical application. The term carrier oil is derived from their purpose in carrying the essential oil onto the skin. Essential oils are distilled from the leaves, bark, roots and other aromatic portions of a botanical, they evaporate and have a concentrated aroma. Carrier oils, on the other hand, are pressed from the fatty portions (seeds, nuts, kernels) and do not evaporate or impart their aroma as strongly as essential oils.