Essential Oils have become immensely popular over the last decade or so. They are complex substances comprised of hundreds of components that vary in composition, quality and extraction method. They can be found in many products including cleaners and insect repellants, but a high-quality oil can also enhance your health. (KNOW YOUR SOURCE) Many possess antimicrobial, antiviral, antibiotic, anti-inflammatory, and antioxidant properties as well as purported psychogenic effects such as relieving stress, treating depression, and aiding with insomnia. You should be aware of possible risk factors with some, so due diligence is needed, as always. When used properly and responsibly, these babies are mini-miracle workers for many people and certainly worth looking into. 
Check out individual properties of these oils here.