Polypodium leucotomos, a fern native to Central and South America, has been studied as a supportive treatment for psoriasis, primarily in the form of oral extracts. The scientific interest in Polypodium leucotomos centers on its antioxidant and photoprotective properties. Several small-scale clinical studies and laboratory experiments suggest that Polypodium leucotomos extract (PLE) can modulate immune response, reduce inflammation, and protect skin cells from oxidative stress and ultraviolet (UV) radiation, which are relevant mechanisms in the pathogenesis and management of psoriasis.

A handful of randomized controlled trials (RCTs) have assessed PLE as an adjunct to conventional UV phototherapy in psoriasis patients. Results from these studies, though limited in scale and number, indicate that PLE may enhance the efficacy of phototherapy, leading to faster clearance of psoriatic lesions and potentially reducing the dose of UV radiation required. The proposed mechanisms behind these effects include inhibition of pro-inflammatory cytokines, reduction of DNA damage, and stabilization of the skin barrier.

While these findings are promising, the overall clinical evidence is still preliminary. Most studies have small sample sizes, short follow-up periods, and are often industry-sponsored. Large, independent, and well-controlled trials are lacking. Thus, PLE is not established as a stand-alone treatment for psoriasis but may be considered as a supportive therapy alongside established interventions, particularly phototherapy. Medical guidelines do not routinely recommend its use due to limited high-quality evidence.