Oregano essential oil has a hot and spicy scent with pungent herbal base notes. It is steam-distilled from the plants’ fresh leaves and twigs, making an extremely potent and clear yellow oil that may be used to support a healthy immune system. This oil is also excellent for promoting fresh air and clean surfaces: try diffusing a drop in your ultrasonic diffuser or add a few drops to cleaning solutions. Oregano commonly causes skin irritation when used in concentrations above 1%.