One of the key active components of the black walnut hull is juglone. Juglone exerts its effect by inhibiting certain enzymes needed for metabolic function. It’s highly toxic to many insect herbivores — it’s often used by organic gardeners as a natural pesticide — and researchers have observed that black walnut can expel parasitic worms from the body.
The tannins in black walnut have an astringent effect, which is used to tighten the epidermis, mucous membranes and relieve irritation. The juice from unripe black walnut hulls has been used in folk medicine for many years as a treatment for topical, localized dermatophytic fungal infections, such as ringworm.
The exocarp of immature green fruit, bark and branches has been used in China to treat liver, lung and gastric cancer. Juglone blocks potassium channels, promotes the generation of hydrogen peroxide and inhibits transcription in cancer cells. it was shown to promote cell death in human colorectal cells, and given black walnuts juglone content, it could make the black walnut a potential cancer fighting food.
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