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Sunscreen and Skin Cancer: An Update

Dr. James Spencer examines the protective effects of sunscreens in the literature and provides a snapshot of questions and answers about sunscreen safety.

James Spencer, MD, is Director, Spencer Dermatology & Skin Surgery Center, St. Petersburg, Florida.

LISTEN to Dr. Spencer discuss the regulatory background of sunscreen ingredients, including testing requirements for systemic effects, and how that influences his recommendations to patients.

“The most important thing we want sunscreens to do is prevent skin cancer. And the answer may surprise you to the simple question: Do sunscreens prevent skin cancer?” said James Spencer, MD, who presented “What’s New in Sunscreens” at the 2022 ODAC Dermatology Conference.

“From animal data, we’re pretty clear that sunscreens prevent actinic keratosis and prevent squamous cell carcinomas. But what about melanoma? What about basal cell [carcinoma]?”

According to Dr. Spencer, the study showing the strongest clinical data that supports sunscreen for melanoma prevention was published in 2011.1

“When you go to sunscreen lectures, they always show this study because it’s the strongest. It’s the one that shows the best evidence.”

The study included 1621 Australians, randomly assigned to one of two groups for five years: 

  1. Daily sunscreen use + 30 mg oral beta carotene 
  2. Discretionary sunscreen use + oral placebo

“Ten years after trial cessation, there were 11 new melanomas in the sunscreen group and 22 in the discretionary group, so this is the strongest study that suggests that melanoma is prevented by sunscreens.”

However, in a more recent literature review of 29 studies including a total of more than 300,000 participants, sunscreen use did not show a decrease in melanoma cases.2

Dr. Spencer noted that sunscreen did not include UVA protection in the 1980s, which may account for an increase in melanoma incidence.

“… sunscreens then didn’t have UVA blockers, but they did have UVB blockers so you didn’t sunburn so you could stay out longer and get more UVA. This effect of increased melanoma disappeared by the 1990s when UVA blockers were added.”

In another review of sunscreen’s protective effects, researchers found scant evidence that it protects against melanoma or basal cell carcinoma (BCC).3 Green et al. also showed regular sunscreen use did not prevent BCC.4

“There’s no question, I think, that [sunscreen] prevents AKs and squamous cell carcinoma; it prevents wrinkles and sagging skin,” said Dr. Spencer. “I think these two reasons alone are enough to recommend sunscreen use, but unfortunately, there’s very little evidence to none, that it prevents melanoma or basal cell carcinoma.”

Sunscreen Safety: A Snapshot

Some concerns have been raised about the safety of sunscreens, said Dr. Spencer, and patients may have questions. 

“I think it’s important for us to have answers to these questions and to reassure patients that sunscreens are a good idea.”

  1. Benzene and sunscreen recalls—Commonly used as an organic solvent, it’s important for patients to know that benzene is not a sunscreen ingredient, said Dr. Spencer. 

“[It’s] probably a contaminant from the manufacturing process.”

  • Estrogenic effect—While animal studies have suggested sunscreen ingredients act like estrogen,5,6human studies have not. 

“… 32 human volunteers applied 2 mg/cm2 with 10% oxybenzone, 4-MBC, and octinoxate over the entire body for four days7—that’s a lot of sunscreen—and no significant hormonal changes were observed.”

  • Systemic absorption—The FDA wanted to know if sunscreen ingredients, including avobenzone, oxybenzone, octocrylene, ecamsule, homosalate, octisalate, and octinoxate, are absorbed by the body. Matta et al. conducted a pilot study8 and follow-on study9 of these ingredients under “maximal use conditions” (2 mg/cm2 sunscreen 4/day for 4 days). The threshold level for maximum plasma concentrations was > 0.5 ng/ml. All study participants had detectable plasma levels above the threshold within one day of sunscreen use. 

“As far as the FDA is concerned, sunscreens are systemically absorbed and therefore we have to consider systemic effects.”

Despite these findings, researchers note that people should continue to use sunscreens.

  • Lower vitamin D levels?—In a review of 76 studies, no effect of sunscreen on vitamin D levels was seen.10

“If your patients are worried about vitamin D, you can tell them sunscreen is okay.”

  • Sunscreens and the environment—Although oxybenzone is an effective UVB blocker, it has been detected in the arctic, the ocean, and the coral reefs, in particular. Contamination may come not only from sunscreen products but also from poorly filtered wastewater facilities and commercial runoff, said Dr. Spencer.

“What should we do when we go to the coral reef? We should consider using zinc or titanium when ocean swimming. Consider protective clothing. And clearly there’s a need for new UV filtering agents.”

Stance on Sunscreens

The two GRASE (generally recognized as safe and effective) sun protection ingredients are zinc oxide and titanium dioxide, said Dr. Spencer. 

“Should we just recommend [these] to avoid all this trouble?”

Notably, said Dr. Spencer, “Consumer Reports testing for 2019 found mineral sunscreens inferior to chemical sunscreens and they wrote, ‘We haven’t been able to find a mineral sunscreen we can recommend.’”

Despite the questions and potential controversy, sunscreen products remain available, and decades of sunscreen use has done more good than not, said Dr. Spencer.

“I think we can reassure our patients that these safety issues are overblown, and sunscreens are safe.”

All things considered, Dr. Spencer said he will continue to recommend his patients use sunscreen.  

“I think we can reassure our patients that …sunscreens are safe, and they are proven beneficial in preventing actinic keratosis, preventing squamous cell carcinoma, and preventing photo aging. And for those reasons alone, sunscreen’s worth using.

References

  1. Green AC, Williams GM, Logan V, Strutton GM. Reduced melanoma after regular sunscreen use: randomized trial follow-up. J Clin Oncol. 2011 Jan 20;29(3):257-63. doi: 10.1200/JCO.2010.28.7078. Epub 2010 Dec 6. PMID: 21135266.
  2. Silva ESD, Tavares R, Paulitsch FDS, Zhang L. Use of sunscreen and risk of melanoma and non-melanoma skin cancer: a systematic review and meta-analysis. Eur J Dermatol. 2018 Apr 1;28(2):186-201. doi: 10.1684/ejd.2018.3251. PMID: 29620003.
  3. Waldman RA, Grant-Kels JM. The role of sunscreen in the prevention of cutaneous melanoma and nonmelanoma skin cancer. J Am Acad Dermatol. 2019 Feb;80(2):574-576.e1. doi: 10.1016/j.jaad.2018.06.069. PMID: 30012373.
  4. Green A, Williams G, Neale R, Hart V, Leslie D, Parsons P, Marks GC, Gaffney P, Battistutta D, Frost C, Lang C, Russell A. Daily sunscreen application and betacarotene supplementation in prevention of basal-cell and squamous-cell carcinomas of the skin: a randomised controlled trial. Lancet. 1999 Aug 28;354(9180):723-9. doi: 10.1016/S0140-6736(98)12168-2. Erratum in: Lancet 1999 Sep 18;354(9183):1038. PMID: 10475183.
  5. Schlumpf M, Cotton B, Conscience M, Haller V, Steinmann B, Lichtensteiger W. In vitro and in vivo estrogenicity of UV screens. Environ Health Perspect. 2001 Mar;109(3):239-44. doi: 10.1289/ehp.01109239. Erratum in: Environ Health Perspect. 2001 Nov;109(11):A517. PMID: 11333184; PMCID: PMC1240241.
  6. Schlumpf M, Jarry H, Wuttke W, Ma R, Lichtensteiger W. Estrogenic activity and estrogen receptor beta binding of the UV filter 3-benzylidene camphor. Comparison with 4-methylbenzylidene camphor. Toxicology. 2004 Jul 1;199(2-3):109-20. doi: 10.1016/j.tox.2004.02.015. PMID: 15147785.
  7. Janjua NR, Kongshoj B, Andersson AM, Wulf HC. Sunscreens in human plasma and urine after repeated whole-body topical application. J Eur Acad Dermatol Venereol. 2008 Apr;22(4):456-61. doi: 10.1111/j.1468-3083.2007.02492.x. Epub 2008 Jan 23. PMID: 18221342.
  8. Matta MK, Zusterzeel R, Pilli NR, Patel V, Volpe DA, Florian J, Oh L, Bashaw E, Zineh I, Sanabria C, Kemp S, Godfrey A, Adah S, Coelho S, Wang J, Furlong LA, Ganley C, Michele T, Strauss DG. Effect of Sunscreen Application Under Maximal Use Conditions on Plasma Concentration of Sunscreen Active Ingredients: A Randomized Clinical Trial. JAMA. 2019 Jun 4;321(21):2082-2091. doi: 10.1001/jama.2019.5586. PMID: 31058986; PMCID: PMC6549296.
  9. Matta MK, Florian J, Zusterzeel R, Pilli NR, Patel V, Volpe DA, Yang Y, Oh L, Bashaw E, Zineh I, Sanabria C, Kemp S, Godfrey A, Adah S, Coelho S, Wang J, Furlong LA, Ganley C, Michele T, Strauss DG. Effect of Sunscreen Application on Plasma Concentration of Sunscreen Active Ingredients: A Randomized Clinical Trial. JAMA. 2020 Jan 21;323(3):256-267. doi: 10.1001/jama.2019.20747. Erratum in: JAMA. 2020 Mar 17;323(11):1098. PMID: 31961417; PMCID: PMC6990686.
  10. Neale RE, Khan SR, Lucas RM, Waterhouse M, Whiteman DC, Olsen CM. The effect of sunscreen on vitamin D: a review. Br J Dermatol. 2019 Nov;181(5):907-915. doi: 10.1111/bjd.17980. Epub 2019 Jul 9. PMID: 30945275.