Essential oils are produced in the leaves of plants and stored in the plant tissue. They are oily, slightly evaporating extracts which, depending on the plant of origin, have a strong, characteristic odor.
Unlike fat oils, they evaporate completely. However, they are also fat soluble and composed of many different components such as alcohols, esters, ketones and terpenes.
In the water they are very difficult to soluble. They swim as single drops on the surface of the water.
Essential oils contain herbal substances which have the task of attracting insects for pollination, to keep pests away and to protect against diseases that are caused, for example, by bacteria or fungi. They are the herbal seduction, defense and self-healing substances. The phenols contained in the oregano include Carvacrol and Thymol. Oregano oil has been proven to have a fungicide and antibacterial effect.
Essential oils are extracted from the plant parts by water vapor distillation. After condensation, the substances are separated from the aqueous phase and can be deposited.
(Source: "Essential oils" Wikipedia.de)