Sunscreen Is Protective Against Skin DNA Damage

Dott. Ruben Cazzola

FotoprotezioneSolar radiation is now accepted as a major contributor to the development of skin cancer. An in vivo study has suggested DNA to be the major chromophore for erythema in the 280-340 nm waveband with a peak at approximately 300 nm.1 Photoprotection education includes staying in the shade when outdoors; wearing photoprotective clothing, including a wide-brimmed hat and sunglasses; and applying broad spectrum sunscreen with SPF of 30 or above. The use of sunscreens has been shown to decrease the development of actinic keratosis.2 A 4.5-year study with 8 years of follow-up involving 1621 residents in Nambour, Queensland, demonstrated the beneficial effects of sunscreens. As compared with the control group, individuals who used SPF16 sunscreens had significantly decreased development of squamous cell carcinoma by 38% and the development of basal cell carcinoma was decreased by 25%, although it was not statistically significant.3,4 Individuals in the sunscreen group also had decreased melanoma development when evaluated 10 years after the completion of the 4.5-year active phase of the study.

The molecular basis for the above mentioned clinical effects of sunscreen was reported in an excellent recent systematic analysis by Olsen et al. that thoroughly discusses the experimental, in vivo evidence on sunscreen’s ability to mitigate keratinocyte and melanocyte DNA damage from ultraviolet radiation.6 Although the included studies had heterogeneous designs, all demonstrated a reduction in markers of DNA damage with topical sunscreen use. The authors mentioned an exponential increase in SPF with application thickness of sunscreen; however, a linear association between the same has been recently demonstrated.7 The discrepancy in the behavior depends on the spectral output of the light source used with a UVB only light source resulting in the exponential response. 

In addition, visible light (400-700 nm), which is a major portion of radiation emitted by the sun, has also been shown to induce biologic effects in dark skinned individuals.8 UV filters in sunscreens do not absorb visible light; studies are ongoing to evaluate other means of protection against the effects of visible light, such as the use of antioxidants.  

Currently, there is strong molecular and clinical evidence regarding the protection by sunscreens against deleterious effects of UVA and UVB radiation. Dermatologists and other care providers therefore should continue to advocate for the use of sunscreens as an integral part of the photoprotective regimen for their patients. 

 References

  1. Young AR, Chadwick CA, Harrison GI, Nikaido O, Ramsden J, Potten CS. The similarity of action spectra for thymine dimers in human epidermis and erythema suggests that DNA is the chromophore for erythema. J Invest Dermatol. 1998;111(6):982-988. http://www.jidonline.org/article/S0022-202X(15)40306-9/fulltext 
  2. Thompson SC, Jolley D, Marks R. Reduction of solar keratosis by regular sunscreen use. N Engl J Med. 1993;329(16):1147-1151. http://www.nejm.org/doi/full/10.1056/NEJM199310143291602 
  3. Green A, Williams G, Neale R, et al. Daily sunscreen application and betacarotene supplementation in prevention of basal-cell and squamous-cell carcinomas of the skin: a randomized controlled trial. Lancet.1999;354(9180):723-729. http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(98)12168-2/fulltext 
  4. van der Pols JC, Williams GM, Pandeya N, et al. Prolonged prevention of squamous cell carcinoma of the skin by regular sunscreen use. Cancer Epidemiol Biomarkers Prev. 2006;15(2):2546-2548. http://cebp.aacrjournals.org/content/15/12/2546.long 
  5. Green AC, Williams GM, Logan V, Strutton GM. Reduced melanoma after regular sunscreen use: randomized trial follow-up. J Clin Oncol. 2011;29:257-263. http://ascopubs.org/doi/full/10.1200/JCO.2010.28.7078 
  6. Olsen CM, Wilson LF, Green AC, Biswas N, Loyalka J, Whiteman DC. Prevention of DNA damage in human skin by topical sunscreens. Photodermatol Photoimmunol Photomed. 2017 Feb 6. doi: 10.1111/phpp.12298. [Epub ahead of print] http://onlinelibrary.wiley.com/wol1/doi/10.1111/phpp.12298/full 
  7. Ou-Yang H, Stanfield J, Cole C, et al. High-SPF sunscreens (SPF ≥ 70) may provide ultraviolet protection above minimal recommended levels by adequately compensating for lower sunscreen user application amounts. J Am Acad Dermatol. 2012; 67:1220-1227. http://www.jaad.org/article/S0190-9622(12)00260-5/fulltext 
  8. Mahmoud BH, Ruvolo E, Hexsel CL, et al. Impact of Long-Wavelength UVA and Visible Light on Melanocompetent Skin. J Invest Dermatol. 2010;130:2092-2097. http://www.jidonline.org/article/S0022-202X(15)34930-7/fulltext 

Henry W Lim MD  James L Griffith MD  Indermeet Kohli MD