Phenolic diterpenes, such as carnosic acid and carnosol, are primarily found in plants like Rosmarinus officinalis (rosemary) and Salvia officinalis (sage). There is emerging scientific interest in their anti-inflammatory and antioxidant properties, which are relevant to psoriasis, a chronic inflammatory skin disease. Several in vitro and animal studies have shown that phenolic diterpenes can modulate inflammatory pathways, specifically by inhibiting NF-κB activation and reducing the production of pro-inflammatory cytokines such as TNF-alpha, IL-1β, and IL-6. These actions suggest a potential mechanism by which phenolic diterpenes could alleviate psoriatic inflammation.

However, clinical evidence in humans is limited. While topical and oral extracts containing phenolic diterpenes are being explored, no large-scale randomized controlled trials have unequivocally demonstrated their efficacy in treating psoriasis. Most evidence is preclinical, with a few small pilot studies and case reports suggesting potential benefit but lacking statistical power or rigorous controls. Thus, the use of phenolic diterpenes for psoriasis is scientifically plausible and supported by basic research, yet robust clinical validation is lacking.

In summary, phenolic diterpenes have a scientific rationale for use in psoriasis due to their anti-inflammatory effects, but current evidence supporting their clinical effectiveness is weak (rated 2/5).