As stated in the guide, Essential Oils (EOs) are extracted by means of cold pressing, steam extraction, or solvent extraction. Oil purities and qualities will vary depending upon the materials used for extraction, the extraction method used, and upon whether any distillation or purification is performed after extraction. Essential Oils are used by the food and fragrance industries. These oils are also used by individuals for homeopathic medical reasons, for aromatherapy, and for massage and spa treatments. Medical doctors in Europe have been using EOs for several years and some doctors in the US are incorporating their use, as well. If using an essential oil for homeopathic, massage, or spa treatment, the oil should be tested on a small patch of skin of an individual prior to using the oil. It is generally recommended that an essential oil be diluted first with a carrier oil, such as grapeseed oil, olive oil, almond oil, or another carrier oil, and tested on a patch of skin on the inside of the forearm. If no reaction occurs within half an hour, the oil should be safe for use on the individual tested. Always try to use the highest purity oils for personal use.