The use of walnut (Juglans regia), particularly its leaves and sometimes the oil, for the treatment of skin conditions like psoriasis is primarily rooted in traditional medicine rather than supported by robust scientific evidence. Historical records from various herbal traditions, including those in Europe and Asia, document the topical application of walnut leaf extracts for the management of chronic skin diseases such as eczema, acne, and psoriasis. The rationale behind this usage is attributed to the anti-inflammatory, antimicrobial, and astringent properties believed to be present in the leaves and hulls due to compounds like juglone, tannins, and flavonoids.

However, scientific validation for the effectiveness of walnut in treating psoriasis is limited. A small number of in vitro and animal studies suggest walnut extracts possess anti-inflammatory and antioxidant properties, which could theoretically benefit inflammatory skin disorders. Nevertheless, there are no well-designed clinical trials providing conclusive evidence for its efficacy or safety specifically in the context of psoriasis in humans. Thus, while traditional use exists, the evidence base is weak and does not support walnut as a standard or reliable treatment for psoriasis.