Plantain is a vulnerary plant, this means it helps regenerate the skin, encouraging cells growth, and has wound healing properties. It has the ability to stop bleeding and heal bruises and it is a great first aid ally when in the wild. It helps with "puncture wounds, bug bites, bee, wasp, and nettle stings, boils and ulcers. When treating cuts and other open wounds, it not only staunches the bleeding, it also prevents infection by removing dirt, and as an antiseptic it disinfects the wound."
It is traditionally used to support lung health. Plantain leaves are rich in mucilage, leaving a protective and demulcent coating on the respiratory tract.
Plantain leaves have a soothing effect on the lungs due to containing glycerine and pectin which have natural demulcent properties. It also helps to restore the protective coating of mucous membranes to a damaged stomach lining, protecting against ulcers.
Its leaves also have vitamins A and C, and are also high in tannin content this has an astringent effect which helps reducing inflammation and combating infection by depriving bacteria of nutrients.  
Plantain can be used to provide natural relief from sunburn, to treat acne and rosacea and to keep the skin healthy, glowing and blemish free.

References

Indigo-Herbs UK
The Gaia School of Healing and Earth Studies