Juglans nigra L., commonly known as black walnut, is a deciduous tree belonging to the Juglandaceae family. It is native to eastern and central North America and has been used historically by Native American communities and later by European settlers for medicinal, household and practical applications.

Different parts of the plant have traditionally been used for different purposes, including the bark, leaves, green fruit hulls and mature seeds. The chemical composition and biological activity of these plant parts can differ substantially, and therefore information relating to one part of the plant should not automatically be applied to another.

Traditional Uses

Black walnut has an extensive history of traditional use. Native Americans and settlers used preparations of the plant as laxatives and tonics. Traditional applications included the use of bark preparations for constipation and fruit-derived preparations for intestinal worms.

The bark, leaves and fruit hulls were also traditionally used in preparations associated with skin complaints, wounds, inflammation, eczema, herpes and fungal infections such as ringworm. Infusions and washes made from the leaves or bark were used externally as cleansing or astringent preparations.

The oil obtained from mature seeds was traditionally applied externally to wounds and various skin conditions.

These uses represent traditional and ethnobotanical applications and should not be interpreted as evidence that black walnut preparations are clinically proven to treat these conditions.

Cosmetic Applications

Juglans nigra-derived ingredients may be relevant to cosmetic formulations depending on the specific plant part and extraction method used. Black walnut extracts, hull-derived ingredients and seed oil can provide different functional properties and should therefore be treated as distinct cosmetic raw materials.

Black walnut seed oil can function as a plant-derived emollient and skin-conditioning ingredient. Extracts from the leaves, bark or hulls may contain tannins, phenolic compounds and other constituents that can contribute to their astringent or antioxidant characteristics.

Green walnut hulls are particularly rich in tannins and have traditionally been used in preparations associated with skin cleansing and coloring.

Seed Oil

The oil obtained from mature Juglans nigra seeds is a lipid-rich plant oil that can be used externally as an emollient and skin-conditioning material.

As with other botanical oils, its fatty acid composition can vary according to cultivar, geographical origin, growing conditions, maturity and extraction method. The specific technical specification of the raw material should therefore be consulted when developing a cosmetic formulation.

Black walnut seed oil may be incorporated into creams, lotions, balms, facial oils and other oil-based formulations where a botanical emollient is desired.

Skin-Related Traditional Use

Black walnut has historically been associated with topical preparations for various skin complaints. Traditional preparations of the bark, leaves and green hulls were used for conditions described historically as eczema, herpes, ringworm, wounds and inflammation.

The green hull and bark contain significant amounts of tannins and other phenolic compounds. These compounds may contribute to astringent and antimicrobial activity observed in experimental research.

Modern cosmetic formulations should distinguish between traditional use and scientifically demonstrated cosmetic benefits. A traditional application does not by itself substantiate a therapeutic claim for a finished cosmetic product.

Antimicrobial and Antifungal Properties

Black walnut has been investigated for antimicrobial and antifungal activity, particularly in relation to extracts of the hull, bark and other non-oil plant parts.

The naphthoquinone juglone is one of the characteristic constituents associated with Juglans species and has demonstrated antimicrobial and biological activity in experimental studies. Tannins and other phenolic constituents may also contribute to the biological activity of black walnut preparations.

However, the concentration and composition of these compounds vary considerably between plant parts and extraction methods. Results obtained using concentrated extracts should therefore not automatically be attributed to black walnut seed oil.

Antioxidant Properties

Black walnut plant materials contain phenolic compounds and other constituents with antioxidant activity in laboratory studies. Green hulls, bark and leaves may contain particularly significant levels of phenolic compounds and tannins.

The antioxidant properties of a finished cosmetic ingredient depend on the specific extraction process, standardization, concentration and stability of the resulting raw material.

Formulation Considerations

The appropriate formulation approach depends on whether the raw material is black walnut seed oil, a leaf extract, bark extract or hull extract. These materials have substantially different compositions and should not be treated as interchangeable.

Black walnut seed oil can be incorporated into the oil phase of emulsions or used in anhydrous formulations. Extracts may require different solvent systems and may have a significant influence on the color, odor and stability of the finished formulation.

Hull and bark extracts can contain tannins and other strongly colored constituents, which may affect the appearance of the finished product. Their compatibility with other formulation components and packaging should therefore be evaluated during product development.

Stability

The stability of Juglans nigra-derived ingredients depends on the specific plant part, extraction method and formulation system.

For seed oil, oxidation should be considered because the unsaturated fatty acids present in the oil can undergo oxidative degradation when exposed to oxygen, heat and light. Appropriate antioxidant protection and packaging may be considered according to the raw material specification.

Extracts containing phenolic compounds and tannins may also be sensitive to environmental conditions and interactions with other formulation components.

Finished formulations should undergo appropriate stability testing to evaluate changes in color, odor, appearance, pH, viscosity, microbial quality and other relevant parameters.

Safety

Black walnut contains biologically active compounds, and safety considerations depend strongly on the plant part and preparation used.

Juglone, tannins and other constituents found particularly in the hulls, bark and leaves contribute to the biological activity of the plant. These compounds also mean that concentrated extracts should not automatically be considered equivalent to the relatively mild traditional use of the whole plant.

Topical products containing black walnut-derived ingredients should be evaluated according to the concentration, extraction method, purity and intended exposure. Particular care should be taken when using concentrated extracts in leave-on products.

The safety profile of black walnut seed oil should not be inferred from toxicological data relating to bark, hull or leaf extracts.

Traditional and Other Uses

Black walnut has historically been used for numerous non-cosmetic purposes. The green hulls, bark and leaves have been used as sources of natural dyes, particularly brown and yellow pigments. The high tannin content of the hulls makes them particularly suitable for dyeing.

The shells have also been used for practical and decorative applications, including jewelry and charcoal. Ground walnut shell material has historically been used as an abrasive and filtration material.

Black walnut is also well known for its allelopathic properties. Roots, leaves and other plant parts produce compounds, particularly juglone, that can inhibit the growth of certain neighboring plants. This natural chemical defense is one of the characteristic biological properties of Juglans species.

Regulatory Considerations

The regulatory status of Juglans nigra-derived ingredients depends on the specific plant part, extraction method, intended use and target market.

When developing a cosmetic product, the exact botanical identity and plant part should be confirmed together with the supplier's INCI designation, extraction method, specification and safety documentation.

Traditional medicinal claims such as treatment of fungal infections, wounds, inflammation or other diseases should not be used for a cosmetic product unless permitted under the applicable regulatory framework.

References

Dweck, Anthony. Handbook of Natural Ingredients. Dweck Books.

European Medicines Agency. Juglans regia L., folium – European Union herbal monograph.

National Center for Biotechnology Information. PubChem – Juglone.

National Center for Biotechnology Information. PubMed – Juglans nigra and juglone.

European Commission. CosIng – Cosmetic Ingredients Database.

U.S. Department of Agriculture. Juglans nigra L. – Black Walnut.

Bhatia, K. et al. Research on the phytochemistry and biological activities of Juglans nigra and its constituent juglone.

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