While searching for an answer to the above, I found the following two quotes in www.aromaweb.com . "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. If applied to the skin undiluted, essential oils, absolutes, CO2s and other concentrated aromatics can cause severe irritation or reactions in some individuals." "Carrier oils are generally not necessary when using most types of diffusers." So why not put just plain essential oil in wax to make tarts? Isn't the carrier oil just adding complexity and cost? Frank