Eucalyptus oil comes from the leaves and branches of the Eucalyptus globulus tree. It was used by Aboriginal Australians to treat colds and respiratory illnesses. Eucalyptus oil has strong germicidal, antibacterial, and anti-inflammatory properties that make it effective for treating respiratory conditions, pain, fever, and wounds. It can be used in a diffuser, chest rub, or diluted in a carrier oil and massaged on the skin. Potential side effects include skin irritation, so it should be kept away from young children.