While it's considered a weed by most gardeners, its flowers and leaves are often used by herbalists to treat respiratory problems and skin conditions.
 
Certain compounds in mullein's leaves and flowers are thought to act as a demulcent, which is a substance that relieves irritation in the body's mucus membranes such as the nose, mouth, and throat. A mullein treatment may also work as an expectorant, which is what a common cough medicine is.
 
In some cases, mullein is applied directly to the skin to help treat burns or skin inflammation. Mullein oil is also used in ear drops for the treatment of ear infections.
 
Mullein helped kill certain types of bacteria, including Staphylococcus aureus (the most common cause of staph infections) and Escherichia coli (or E. coli).
 
Upper respiratory tract infections
Coughs
Bronchitis
Asthma
Flu 
In test-tube research, mullein has been found to fight flu-causing viruses.
 
https://www.verywellhealth.com/the-benefits-of-mullein-89575