JOURNAL OF COSMETIC SCIENCE 222 erythema is much lower by facultative tanning in white skin types. A comparison of FST II versus VI shows that melanin has a very modest inhibitory effect on vitamin D photo- synthesis. Melanin protection/inhibition against a given target depends on spatial rela- tionships within the epidermis. Sunscreen protection against erythema depends on its the SPF and application thickness. Used correctly, sunscreens will inhibit erythema in “real- life” situations. There is good experimental evidence that sunscreens will inhibit DNA photodamage and skin cancer. However, to get the equivalent of constitutive protection against skin cancer, it is likely that FST I/II would need an SPF about 60. Sunscreens have a relatively modest effect on vitamin D synthesis. Better sunscreen protection would be achieved with better use. ACK NOWLEDGMENTS I t hank Dr. Paulo Giacomoni for the invitation to contribute to this special edition on sunscreens. It has given me an opportunity to present much of my work on photoprotec- tion over the past few decades. I would also like to thank the many colleagues and stu- dents who made this work possible. REF ERENCES (1 ) M. Bustamante, C. Hernandez-Ferrer, A. Tewari, Y. Sarria, G. I. Harrison, E. Puigdecanet, L. Nonell, W. Kang , M. R. Friedländer, X. Estivill, J. R. González, M. Nieuwenhuijsen, and A. R. Young, Dose and time effects of solar-simulated ultraviolet radiation on the in vivo human skin transcriptome, Br. J. Dermatol., 182, 1458–1468 (2020). (2) M. Bustamante, C. Hernandez-Ferrer, Y. Sarria, G. I. Harrison, L. Nonell, W. Kang, M. R. Friedländer, X. Estivill, J. R. González, M. Nieuwenhuijsen, and A. R. Young, The acute effects of ultraviolet ra- diation on the blood transcriptome are independent of plasma 25OHD3, Environ. Res., 159, 239–248 (2017). (3) M. Bustamante, V. Wucher, and A. R. Y oung, Importance of considering circadian rhythm in the design of in vivo transcriptional studies of acute effects of environmental exposures: commentary to “The acute effects of ultraviolet radiation on the blood transcriptome are independent of plasma 25OHD3”, pub- lished in Environmental Research 2017 Nov:159: 239–248. doi: 10.1016/j.envres.2017.07.045, Envi- ron. Res., 178, 108691 (2019). (4) R. B. Weller, Y. Wang, J. He, F. W. M addux, L. Usvyat, H. Zhang, M. Feelisch, and P. Kotanko, Does incident solar ultraviolet radiation lower blood pressure? J. Am. Heart Assoc., 9(5), e013837 (2020). (5) D. Fajuyigbe and A. R. Young, The im p act of skin colour on human photobiological responses, Pigment Cell Melanoma Res., 29(6), 607–618 (2016). (6) A. R. Young, C. S. Potten, C. A. Cha d wick, G. M. Murphy, J. L. Hawk, and A. J. Cohen, Photoprotec- tion and 5-MOP photochemoprotection from UVR-induced DNA damage in humans: the role of skin type, J. Invest. Dermatol., 97(5), 942–948 (1991). (7) A. R. Young, S. L. Walker, J. S. Kin l ey, S. R. Plastow, D. Averbeck, P. Morliere, and L. Dubertret, Phototumorigenesis studies of 5-methoxypsoralen in bergamot oil: evaluation and modifi cation of risk of human use in an albino mouse skin model, J. Photochem. Photobiol. B, 7(2–4), 231–250 (1990). (8) L. M. Fitzgerald, J. L. Fryer, T. Dw y er, and S. M. Humphrey, Effect of MELANOTAN, [Nle(4), D- Phe(7)]-alpha-MSH, on melanin synthesis in humans with MC1R variant alleles, Peptides, 27(2), 388– 394 (2006). (9) N. G. Jablonski and G. Chaplin, The e volution of human skin coloration, J. Hum. Evol., 39(1), 57–106 (2000). (10) N. G. Jablonski and G. Chaplin, Col l oquium paper: human skin pigmentation as an adaptation to UV radiation, Proc. Natl. Acad. Sci. U.S.A., 107(Suppl. 2), 8962–8968 (2010). (11) R. L. McKenzie and R. M. Lucas, Rea s sessing impacts of extended daily exposure to low level solar UV radiation, Sci. Rep., 8(1), 13805 (2018).

SKIN PHOTOPROTECTION BY PIGMENTATION AND SUNSCREENS 223 (12) U. Osterwalder, M. Sohn, and B. Her z og Global state of sunscreens, Photodermatol. Photoimmunol. Pho- tomed., 30(2–3), 62–80 (2014). (13) M. Charalambides, N. Kibbi, and A. R . Young, Effect of sunscreen application under maximal-use conditions on plasma concentration of sunscreen active ingredients: a critical appraisal, Br. J. Dermatol., 182, 1345–1347 (2020). (14) A. R. Young, J. Claveau, and A. B. R ossi, Ultraviolet radiation and the skin: photobiology and sun- screen photoprotection, J. Am. Acad. Dermatol., 76(3S1), S100–S109 (2017). (15) B. Diffey and U. Osterwalder, Label l ed sunscreen SPFs may overestimate protection in natural sunlight, Photochem. Photobiol. Sci., 16(10), 1519–1523 (2017). (16) A. Tewari, R. P. Sarkany, and A. R. Young, UVA1 induces cyclobutane pyrimidine dimers but not 6-4 photoproducts in human skin in vivo, J. Invest. Dermatol., 132(2), 394–400 (2012). (17) K. P. Lawrence, T. Douki, R. P. E. S arkany, S. Acker, B. Herzog, and A. R. Young, The UV/visible ra- diation boundary region (385–405 nm) damages skin cells and induces “dark” cyclobutane pyrimidine dimers in human skin in vivo, Sci. Rep., 8(1), 12722 (2018). (18) J. Narbutt, P. A. Philipsen, G. I. Harrison, K. A. Morgan, K. P. Lawrence, K. A. Baczynska, K. Grys, M. Rogowski-Tylman, I. Olejniczak-Staruch, A. Tewari, M. Bell, C. O’Connor, H. C. Wulf, A. Lesiak, and A. R. Young, Sunscreen applied at /= 2 mg cm(-2) during a sunny holiday prevents erythema, a biomarker of ultraviolet radiation-induced DNA damage and suppression of acquired immunity, Br. J. Dermatol., 180(3), 604–614 (2019). (19) B. Petersen, H. C. Wulf, M. Triguero-Mas, P. A. Philipsen, E. Thieden, P. Olsen, J. Heydenreich, P. Dadvand, X. Basagaña, T. S. Liljendahl, G. I. Harrison, D. Segerbäck, A. W. Schmalwieser, A. R. Young, and M. J. Nieuwenhuijsen, Sun and ski holidays improve vitamin D status, but are associated with high levels of DNA damage, J. Invest. Dermatol., 134(11), 2806–2813 (2014). (20) J. Narbutt , P. A. Philipsen, A. Lesiak, T. Sandberg Liljendahl, D. Segerback, J. Heydenreich, D. Chlebna-Sokol, P. Olsen, G. I. Harrison, A. Pearson, K. Baczynska, M. Rogowski-Tylman, H. C. Wulf, and A. R. Young, Children sustain high levels of skin DNA photodamage, with a modest increase of serum 25-hydroxyvitamin D3, after a summer holiday in northern Europe, Br. J. Dermatol., 179(4), 940–950 (2018). (21) D. E. Bras h , UV signature mutations, Photochem. Photobiol., 91(1), 15–26 (2015). (22) H. Fassihi , M. Sethi, H. Fawcett, J. Wing, N. Chandler, S. Mohammed, E. Craythorne, A. M. S. Morley, R. Lim, S. Turner, T. Henshaw, I. Garrood, P. Giunti, T. Hedderly, A. Abiona, H. Naik, G. Harrop, D. McGibbon, N. G. J. Jaspers, E. Botta, T. Nardo, M. Stefanini, A. R. Young, R. P. E. Sarkany, and A. R. Lehmann, Deep phenotyping of 89 xeroderma pigmentosum patients reveals unexpected hetero- geneity dependent on the precise molecular defect, Proc. Natl. Acad. Sci. U.S.A., 113(9), E1236–E1245 (2016). (23) D. Fajuyig b e, S. M. Lwin, B. L. Diffey, R. Baker, D. J. Tobin, R. P. E. Sarkany, and A. R. Young, Mela- nin distribution in human epidermis affords localized protection against DNA photodamage and con- curs with skin cancer incidence difference in extreme phototypes, FASEB J., 32(7), 3700–3706 (2018). (24) G. I. Harr i son and A. R. Young, Ultraviolet radiation-induced erythema in human skin, Methods, 28(1), 14–19 (2002). (25) D. Fajuyig b e, A. Coleman, R. P. E. Sarkany, A. R. Young, and A. W. Schmalwieser, Diffuse refl ectance spectroscopy as a reliable means of comparing ultraviolet radiation-induced erythema in extreme skin colors, Photochem. Photobiol., 94(5), 1066–1070 (2018). (26) B. B. Shih , D. Allan, F. R. de Gruijl, and L. E. Rhodes, Robust detection of minimal sunburn in pig- mented skin by 785 nm laser speckle contrast imaging of blood fl ux, J. Invest. Dermatol., 135(4), 1197– 1199 (2015). (27) N. Agar an d A. R. Young, Melanogenesis: a photoprotective response to DNA damage? Mutat. Res., 571(1–2), 121–132 (2005). (28) J. M. Shee h an, C. S. Potten, and A. R. Young, Tanning in human skin types II and III offers modest photoprotection against erythema, Photochem. Photobiol., 68(4), 588–592 (1998). (29) J. M. Shee h an, N. Cragg, C. A. Chadwick, C. S. Potten, and A. R. Young, Repeated ultraviolet exposure affords the same protection against DNA photodamage and erythema in human skin types II and IV but is associated with faster DNA repair in skin type IV, J. Invest. Dermatol., 118(5), 825–829 (2002). (30) M. Garmyn, A. R. Young, and S. A. Miller, Mechanisms of and variables affecting UVR photoadapta- tion in human skin, Photochem. Photobiol. Sci., 17(12), 1932–1940 (2018). (31) B. Peterse n , P. Datta, P. A. Philipsen, and H. C. Wulf, Sunscreen use and failures—on site observations on a sun-holiday, Photochem. Photobiol. Sci., 12(1), 190–196 (2013).