How do essential oils work?
-applied to the skin: At the right dillution with a carrier oil
-inhaled: to the lungs, going to the bloodstream, circulate through the body, acting direct in some organs. Not a proven theory
by the olfactory system : Interaction with the limbic system, or the "emotional brain" . Well tested, by EEG, lavender can raise alpha waves, calming us, others are energizers.
-ingested: only trained physicians and pharmacists can prescribe and dispense them. Although infutions of spearmint and other herbs is a common practice for all of us.

Here I will just talk about their uses in massages, and inhalation, their properties, positives and negatives. We want to feel better, with a warm smell in winter, fresh in summertime, help us with our mood changes, stress, help with our aches, prevent some diseases.
The very first blend I use was for my headaches, and they really worked, then came the "Four thieves blend", funny name, but it is a strong disinfictant, used in a diffussor it helps to prevent colds, flu, and other diseases.
"Smell is a potent wizard that transport us across thousands of miles and all years we have lived" Helen Keller