Essential oils have most likely been used by people—for healing, for beautification, and for spiritual enhancement for centuries. The plants that people have found beneficial for essential oil distillation evolved right alongside our pre-Homo sapiens ancestors.
As we are rediscovering essential oils, many questions arise: why would I use them? How do I use them? Are they safe? Having studied and experimented with (therapeutic grade) essential oils for fourteen years, I feel confident stating that, yes, they are safe (with several cautions); using the oils is a delicious experience and one that can protect you from viruses, bacteria and the other bad “crud” that is out there; and there seems to be no end to the ways essential oils can be used.
It is important to differentiate between pure, therapeutic-grade essential oils and the many “aromatherapy” products out there that are mainly used for fragrance and may be adulterated with lesser-grade oils, alcohols, and even petroleum products. Knowing where your oils come from--who grew the plants, who distilled them, how and where they were tested--is critical to assure that you have a pure product that is safe to use. Best case is to have a trusting relationship with the company that provides your oils, but, when in doubt, follow your nose. As you use good-quality essential oils, you will begin to develop a good olfactory sense for what is real and what has been tampered with.

A quick run-down of some of the ways you can use essential oils:
Inhalation. A drop or two in your palm, rub palms together and cup over your nose. You could also use a diffuser to disperse oil molecules in a room; be sure to use one that does not involve heat or you will destroy the oil’s therapeutic properties.
Topical application. To guard against skin sensitivities, dilute oil 1:1 with pure vegetable oil such as almond or olive. Key points of application on the body are crown of head, temples, neck, abdomen, soles and tops of feet, and over vital organs. With additional dilution (20:1 or more), most oils can be incorporated into a full-body massage.
Internal consumption. Research indicates that some oils are more effective when taken orally. Only pure essential oils, proven safe and labeled as dietary supplements, should be used internally. Consult the literature to determine which oils meet the GRAS (generally regarded as safe) standard. To consume, put several drops in a gelatin capsule, 1-2 drops in a glass of water or a teaspoon of agave, or add 1 drop to a meal at the end of cooking.

The joys of using essential oils could be summed up in this statement from Aroma, The International Magazine for Essential Oils: “For most people, a lifestyle that incorporates essential oils leads to a new view of reality, one in which manufactured substitutes for flavor, fragrance, art, and other aspects of the sensory world lose their importance and the original beauty of life can be rediscovered.”