4.      http://www.dailymail.co.uk/health/article-2467385/Suns-UV-rays-account-80-cent-skin-wrinkles-ageing.html

5.       http://news.yale.edu/2015/02/19/sunlight-continues-damage-skin-dark

6.      Phillips, T J., et al. "Hormonal effects on skin aging." (2001): 661-672.

7.       Andrea Vierkötter* and Jean Krutmann. Environmental influences on skin aging and ethnic-specific manifestation, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3583881/

8.      Art Papier, Skin health is directly related to stress, http://www.sheknows.com/health-and-wellness/articles/810077/how-stress-is-damaging-your-skin

9.      Middelkamp-Hup MA et al. Oral Polypodium leucotomos extract decreases ultraviolet-induced damage of human skin. J Am Acad Dermatol. 2004 Dec;51(6):910-8.

10.  Tanew A et al. Oral administration of a hydrophilic extract of Polypodium leucotomos for the prevention of polymorphic light eruption. J Am Acad Dermatol. 2011 Jun 20. [Epub ahead of print]

11.  Caccialanza, M., et al. "Oral polypodium leucotomos extract photoprotective activity in 57 patients with idiopathic photodermatoses." G Ital Dermatol Venereol (2011):85-7.

12. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3062212/

14. http://vietnamnet.vn/vn/doi-song/287843/cau-truc-nen-quyet-dinh-nhan-sac-lan-da.html

16. http://cand.com.vn/doi-song/Hong-da-vi-lam-dep-sai-cach-381782/