Thieves is a blend of essential oils that every oil company offers. If you don’t know what Thieves oil blend is, let me briefly explain. This essential oil blend is made up of lemon, rosemary, cinnamon, eucalyptus and clove. These 5 essential oils are powerful when it comes to killing germs internally, airborne and on surfaces. It is most commonly used in a diffuser during the winter season when colds and flus take hold easily.