Pure essential oils are designed to be diffused and inhaled. You can go to a health store such as Whole Foods or Wild Oats. They have a section of oils that you can smell right there and see if you like it. They have therapeutic value in addition to the scent. Usually there is someone there who can tell you which ones can be used in a diffuser. There are some that can gum up the diffuser. You don't want these in contact with your atomizer.
Again, if you do it yourself you will know that you are getting quality product.
When the oil has quality you need very little and it goes a long way.
The oils come in natural and synthetic version.
Natural ones found in the stores above are beneficial to the body.
Synthetic versions of these same oils such as found in air fresheners at Wal-mart are toxic to the body used long term. This was even featured in Consumer Reports.
This is why you want to avoid operators who offer their own cheap flavorings of unknown origin. Usually these flavors are petroleum based, they don't last, the flavor goes away fast and they are damaging to the atomizer.
