The olfactory nerves that give us the sense of smell is the “only one of all human senses to connect directly to the forebrain; the area that is responsible for cognitive, auditory, sensory, and visual information, as well as being involved in the forming and storage of memory and emotion” (source). In other words, our sense of smell is a straight line to the storage bank of past lives (memory) and our feelings of, for example: fear, anger, or love, joy, and peace (emotion).
Inhalation is the quickest method of introducing a substance to the brain and therefore has the most effective ability of all methods in creating a chemical change (hormone) within your body. Chemicals (hormones) cause emotions. Thoughts cause chemical reactions (as well as a measurable vibrational frequency) that cause emotions.
Diffusing Young Living essential oils is so effective because they immediately enter the blood stream through the olfactory system.