Many essential oils, including lavender, ylang-ylang, patchouli, clove, vanilla, and peppermint may already be found in any ordinary garden or in your kitchen cabinets. You may have also seen them on the labels of many cleaning products, especially those that feature the buzzwords "all-natural," "hypoallergenic," and "organic." A word of caution, though: Just because something is natural, it isn't necessarily hypoallergenic. Some people are allergic to even all-natural products.

Essential oils are quite versatile. They are mostly plant-derived, with the exception of musk, which is taken from the musk glands of a large mammal -- usually the musk ox. The plant-based essential oils are extracted from the leaves, stems, or stalks of the plant through a process of cold- or hot-pressing. For centuries, plants have been used for their different effects on the human body. As more and more people look for greener alternatives for their lifestyles, the many uses of essential oils -- everything from aromatherapy to cleaning and pest control -- have had a resurgence in popularity. Much like the Fantastic Four ingredients of green cleaning (vinegar, salt, lemon juice and baking soda), there is the fabulous core group of essential oils: eucalyptus, lavender, peppermint, and citrus.

Essential oils can be suspended in another inert oil, such as mineral oil or another plant-based oil like carrot or apricot seed oil. They can also be combined in a solution with rubbing alcohol and witch hazel. They can't be used with water, since, as you might remember from high school chemistry class, oil and water do not mix. Essential oils can also be used with the Fantastic Four in various household tasks or added to lotions and salves -- just don't apply them directly to laundry or they'll stain. In some cases (though not for people who are allergic, are in early pregnancy, or are nursing), oils are safe to inhale or ingest. Of course, make sure to research the safety of an oil first and use where appropriate.

Now, let's take a closer look at these four oils.