Usnea is a tree lichen used in traditional herbalism on the skin. People apply it to minor cuts, scrapes, and skin irritations.
Some herbal traditions recommend internal use, but oral evidence is thin. Usnic acid, a compound in usnea, raises liver safety concerns. Mainstream sources now advise sticking to topical applications.
You can find usnea as dried herb for teas or tinctures, and in salves and creams. Apply it as a compress, wash, or ointment on the skin. Consult a professional before use.