Star anise oil is eight to nine tenths trans-anethole, the compound behind liquorice and aniseed. That makes it one of the purest oils on the shelf, chemically speaking, with little else to speak of. In lab tests anethole held back a range of fungi.^[1] The oil also stopped food-poisoning bacteria talking to each other and forming biofilms.^[2] Anethole has weak oestrogen-like activity, so this is an oil to use sparingly if hormones are a concern.^[2]