The health benefits of mullein essential oil can be attributed to its properties as an analgesic, anti-inflammatory, antiseptic, disinfectant, diuretic, expectorant, febrifuge, relaxant, and tranquilizing substance.
Common mullein or Verbascum thapsus and wavy leaf mullein or Verbascum sinuatum, as they are botanically known, are both used to extract the essential oil. The former one is more preferred for extracting oil. The essential oil is extracted by steam distillation of its leaves and flowers.
Mullein is distributed all over Europe, South and Central America, and the temperate zones of Asia. The essential oil contains coumarin, rotenone, tannin, triterpene saponins like verbascosaponin, mucilage, aucubin, catalpol, flavonoids, and phenolic acids. From a very long time ago, mullein was famously known as Candlewick, as it as actually was used to make candlewicks.
Later on, its medicinal uses became more important than its original uses. Let us explore more about what those medicinal uses are.
Health Benefits of Mullein Essential Oil
The analgesic property of this oil has a numbing effect on the nerves. It does not let them sense pain and carry the sensation to the brain, thereby giving relief from pains, such as those of a toothache, headache, cold, sinusitis, and others. It does not have adverse side effects on the body as general analgesic pills do.
The essential oil of mullein is anti-inflammatory in nature. It can effectively cure any type of nasal or respiratory tracts inflammation that may result from the common cold or inflammation in the digestive system caused by overeating of spicy food, alcoholic drinks, inflammation of the circulatory system caused by any toxic substance getting into the bloodstream, or inflammations caused by any other reason such as fever or infection. This oil can cure any type of inflammation. 
The antiseptic property of this essential oil gives protection to wounds from infections which may cause septic and tetanus. This, it does by eliminating microbial growth in the affected place and also by activating the white blood cells and platelets in the region, so that microbes, even if they succeed to get through the wounds, are finished by these two agents.
This oil is very efficient in curing both internal and external infections. Internally, it cures infections in the genitals and the urinary tracts, colon, excretory system, and the kidneys. Externally, it fights infections on the skin, in the ear, nose, and other parts of the body.
The mullein essential oil increases urination both by frequency and by quantity. This helps to drain out the toxins like uric acid as well as extra salts, water, and bile deposited in the body. Urination also helps to reduce weight due to the removal of water and fat through urine. It also helps to reduce blood pressure, enhances appetite, promotes digestion and prevents the formation of gases in the intestines. Urination also clears the deposits in the kidneys, thus keeping them clean.
This oil has remarkable expectorant properties. It loosens coughs or phlegm that is deposited in the lungs and respiratory tracts and gives relief from a cough, heaviness in the chest, breathing troubles, asthma, bronchitis, congestion, and other respiratory disorders. It does not only clear depositions of phlegm or catarrh but also soothes the mucous membrane. In fact, mullein was used in traditional Mexican medicine to treat inflammatory illness, particularly of the respiratory tract. 
This essential oil of mullein is also capable of reducing fever by fighting the infections that cause fever. The diuretic properties of this oil also contribute to this effect, since the removal of toxins and wastes from the body speeds up recovery from infections.
Mullein essential oil has relaxing effects on the muscles, nerves, brain, and all other systems, thus giving relief from muscular cramps, nervous afflictions, and disturbances, nervous disorders, stress, anxiety, anger, depressions, etc. This also helps reduce blood pressure and reduces the chances of a heart attack. 
The patients of chronic insomnia or stress-related acute insomnia can definitely benefit from this property of mullein essential oil. It can give them their most desired thing, which is a night of sound sleep.
Apart from the uses discussed above, this oil is used to treat all ailments of the respiratory system, such as congestion and coughs. According to the book, Herbal Medicine: Biomolecular and Clinical Aspects mullein is also effective in treating dermatological disorders, including healing wounds and burns. 
A Few Words of Caution: No potent threat has been noted. It is non-toxic and non-irritant.
Blending: Mullein essential oil blends well with the essential oils of basil, eucalyptus, garlic, and thyme.