A base oil is a lipid-based substance used to dilute essential oils. The most popular base oils are pure vegetable oils, including grapeseed, avocado and almond oils; however, the most readily available base oils can go rancid rather quickly. I prefer fractionated coconut oil because it is stable at all temperatures and in all environments. It is also non-aromatic and therefore does not alter the aromatic properties of essential oils. Many people mistakenly believe that using base oils somehow reduces the effectiveness of the essential oil, when in fact there are many benefits of diluting oils. Dilution increases the surface area of absorption, improves absorption by dry skin and prevents sensitivities. It is never wrong to dilute, especially when using oils with more potent chemistry. Determining when and how to dilute is a personal decision that should be based on preferences for use, oil chemistry and personal sensitivity.