Polypodium leucotomos is a tropical fern plant native to Central America and parts of South America with a long history of usage in herbal remedies for skin health.
Polypodium leucotomos’s antioxidant properties help to inhibit free radicals in skin tissues from causing long-term DNA damage and photo-ageing.
Polypodium leucotomos has been extensively researched. Overall, 19 human and 6 basic science studies were included in this review spanning over 40 years of research from 1972 to 2014. Current level of evidence suggests that oral PLE is safe and can be prescribed confidently for long term use. 
Much of the research that has been done on Polypodium leucotomos over the past 40+ years has been on its management of skin conditions and its photo-protective properties after it is ingested. , , 
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(3) [Caccialanza M, Percivalle S, Piccinno R, Brambilla R. Photoprotective activity of oral polypodium leucotomos extract in 25 patients with idiopathic photodermatoses. Photodermatol Photoimmunol Photomed. 2007 Feb;23(1):46-7.]
(4) Kohli I, Shafi R, Isedeh P, Griffith JL, Al-Jamal MS, Silpa-Archa N, et al. . The impact of oral Polypodium leucotomos extract on ultraviolet B response: a human clinical study. J Am Acad Dermatol.(2017) 77:33–41. 10.1016/j.jaad.2017.01.044 [PMC free article] [PubMed] [CrossRef] [Google Scholar]