Mullein, like most herbs, has commitment issues and does lots of things. It has some anti-inflammatory properties from flavenods and saponins. The leaf also has some mucilage which is good for soothing irritated mucus membranes. It sure makes irritated lungs happy.
Here’s a Qucikview on Mullein
Mullein (Verbascum thapsus)
Don't use herbs or combine herbs with medications or use them during lactation or pregnancy without talking with your healthcare provider.