Isatis tinctoria leaves give this extract, also called woad. Unlike the root, the leaf rarely appears in traditional herbal formulas meant for internal immune support. Today, manufacturers put leaf extract into topical creams and ointments for its soothing, astringent action on minor skin irritation. Early lab work hints that leaf compounds might interact with immune pathways, but no human data confirm oral benefit.
Apply the extract only to skin, in creams or ointments, for occasional discomfort. No oral dose is established for this leaf extract. Reliable absorption and tolerability data for internal use are missing.
Do not use on large open wounds or broken skin. Pregnant or breastfeeding women should avoid taking it internally because safety data are absent. In some people, the leaf may cause skin sensitivity.