Woad (Isatis) has been used in Chinese medicine for 2,000+ years. Many studies have shown it be effective against influenza (the flu). It has also been shown to have antibacterial and anti-parasitic effects, including against leptospirosis. In China, woad is used to treat such conditions as pneumonia, UTI, sinusitis, tonsillitis, influenza and even acute hepatitis. They also brew it into a tea to use topically on rosacea, herpes, shingles, and impetigo.