Frankinscence! Good quality organic, orally.. a few drops in warm water daily. Iodine is also a good idea, even though its not an essential oil, but really worth checking out.
"Frankincense is used to boost immunity, ease depression, reduce inflammation in the respiratory, urinary, and digestive tracts, combat wrinkles and acne, and help heal varicose veins, wounds, and fungal infections"