Essential oils are the fragrance oils extracted from a plant into a concentrated oil that is said to contain the "essence" or "soul" of the plant. In alchemical philosophy, essential oil is the sulfur principle of the plant.

Other names for this are: volitile oil, oil of <whatever plant>, essence of <whatever plant>, aetherolea

Extraction of Essential Oils

Most essential oils are steam distilled. Plant parts- flowers, leaves, stems, bark, roots or fruit peels are placed in an alembic over water which is heated, producing steam, which vaporizes the volatile oils of the plant matter. These flow through the coil and condense back into a liquid. The resulting scented water left over from this process is a hydrosol. While the amounts of essential oil that can be extracted from plant matter in this way varies by plant, the quantity of oil extracted tends to be quite small compared to the parent plant material and the high temperatures used can also damage the oils being extracted.
The Art of Spagyrics:Distillation of Essential Oils

Essential oils can be extracted using mechanical extraction. This is especially used to extract oils from the skin of citrus fruit. The process is similar to that which you would use to get oil from nuts or fruit, like olives. The peels are otherwise a waste product, so these oils tend to be much easier to obtain for much lower prices than steam distilled essential oils.

Solvent extraction uses a chemical solvent to separate essential oils from parent plant matter. The oil is dissolved in a chemical (the solvent) and then further steps can be taken to extract the oil from the solvent. This is the best way for some plant oils, those that are too delicate to tolerate steam distillation or have too small a quantity of oil to plant material for mechanical extraction. Industry has a number of chemical solvents it uses to extract the oils and extra steps that it can take to purify them, but we can also use a simplified version of this method in our kitchens. Those of us extracting oils in our kitchens generally have alcohol and vegetable oils at our disposal. Alcohol is a preferred solvent for several reasons. Most obviously, alcohol does not harbor bacteria or go rancid like vegetable oils do, so there is less worry of spoilage than with an oil solvent. However, if you are extracting oils from a plant to make a massage oil or a salve, you may as well extract it right into the carrier oil you'll be using to save that extra step. You will not get pure essential oils through either of these methods, but essential oils will be in your final product and if you are growing your own herbs, you may prefer to do it this way than to purchase pure essential oils produced by someone else.

Using Essential Oils

Essential oils are used extensively in aromatherapy and anywhere that fragrance is desired.
In magick, fragrance is used often to help create an energetic atmosphere that aligns with the intent of the spell or ceremony being performed. Essential oils can be used to bring fragrance to your situation using a diffuser, by adding it to the candle wax when candles are created for specific magical purposes, but adding it to your dressing oil, or simply spraying it onto you ritual garb or altar cloth.

Many essential oils contain valuable compounds that are useful in medicine and other household uses. Thymol (in thyme and many of its close relatives) is antimicrobial and can be used in household cleaners and disinfectant sprays. Menthol (in mint relatives) causes a cooling sensation and is used as a topical analgesic and inhaled as a decongestant. Capsaicin (in hot peppers) causes a warming sensation and is also used as a topical analgesic.

Safety of Essential Oils

The safety of essential oils varies widely by the oil. Some oils are safe for ingestion and application directly on the skin, but many, most in fact, are not. All essential oils should be kept out of the eyes and away from delicate skin areas and mucous membranes. Some of the most useful oils can cause great discomfort or damage applied to the skin and some are quite poisonous. Most essential oils are diluted into carrier oils or alcohol before use. (Essential oils are not water soluble, so if you add them to water they will not dilute and will cling to your skin as the water washes off.)

I know that people are occasionally advised to drop essential oils under their tongue and to apply pure essential oils directly to an affected area. Some essential oils are safe to use this way, but really very few. It is important that you research the specific oil that you are using and consult an experienced practitioner before using essential oils directly on your skin or ingesting them.

If you do get essential oils onto your skin or mucous membranes and this causes you discomfort, remember that they are oils. Water will not wash them off by itself, it will just flow right over them, maybe bead up if there's a lot. Soap, especially dish soap designed to break up oils will help you wash them off, but rubbing an inert oil (like olive oil, sunflower oil, etc.) into the area will dilute the oil so you can wash it off easier. Flushing the area with an inert oil or fat-containing substance (like whole milk) may also help, as the oil molecules tend to cling to each other and the inert oil can lift the essential oils away. Essential oil will also dissolve in alcohol though alcohol can also be irritating.

If you have gotten essential oil in your eye, you can flush it with milk or cream to get out the oil and then follow up by flushing it with water to get the milk out, but you should also get to the hospital and have that eye looked at ASAP. Essential oils can cause serious damage to the cornea.

If you have ingested essential oil, please call your local poison control center or 1-800-222-1222