If you thought the dispute about vitamin D and sun exposure was complicated, the controversy about ingredients in sunscreens just takes it beyond the pale. Let me state clearly from the beginning that I am as frustrated by the conflicting research as anyone. We know sun damages skin but what are we to do if sunscreen ingredients pose the same problem or worse? The sunscreens under scrutiny include almost all of the synthetic sunscreen ingredients used in SPF products, such as octylmethoxy cinnamate, 4-methylbenzylidene camphor, phenylbenzimidazole, sulphonic acid, and 2-phenylbenzimidazole, padimate-O, homosalate, oxybenzone, avobenzone, butyl methoxydibenzylmethane, benzophone-3, and Mexoryl.

Many of these ingredients are in question because they have the ability to enter the bloodstream and disrupt the endocrine system, which regulates the releases of hormones into the body, or cause cell mutation in vitro. Synthetic sunscreen ingredients can often mimic estrogen, and so the question is how does that affect systems in the body?

Ironically, the endocrine-disrupting potencies of sunscreen ingredients “are several orders of magnitude lower than that of the natural estrogens” (Source: Environment International, July 2007, pages 654–669). Other human endocrine-disrupting sources have a plant origin, such as marijuana (Source: Toxicology, January 2005, pages 471–488), or are found in medicines such as acetaminophen (Tylenol) (Source: Water Research, November 2008, pages 4578–4588).
Another potential detriment for synthetic sunscreen ingredients is that, upon absorption, these can generate free-radical damage. Synthetic sunscreen ingredients interact with the very light they are meant to direct away from skin cells. Several published studies show oxidative damage in vitro from various sunscreen ingredients. But on the other hand, sunscreen also reacts with the UV radiation and traps it, mitigating harmful effects. Some scientists argue that it is just by this trapping of radicals that synthetic sunscreen ingredients offer their protection.

What’s a person to do? Good question, though regrettably there isn’t an easy answer.

In truth, all synthetic sunscreen agents, even nano-particled titanium dioxide and zinc oxide, have some intimidating negative research about their potential effects on skin. These aren’t junk science articles either—they are all from very notable publications involving both in vivo and in vitro experiments, and include reports in such well-respected journals as The Lancet, Journal of Investigative Dermatology,and Mutation Research. Rather than elaborate on each specific paper (which would take pages and pages), let me sum up the major issues.

Some in vitro studies have indicated that there is a possibility that certain sunscreen ingredients can be absorbed into skin, and there are a handful of in vivo studies as well. However, there are still many researchers who believe that most sunscreen ingredients stay on the surface of skin (where skin cells are dead) and do not penetrate into the lower layers of skin where the real damage occurs. If that’s the case, it means the negative effects seen for surface skin in test tube studies may be irrelevant. Even when absorption has been shown, the related risk has not been demonstrated.

All these issues are significant and deserve more research, but none of the findings indicate that anyone should give up using sunscreen or that the presence of these substances is causing problems. Besides, it is important to realize that no one sunscreen ingredient stands out as more of a potential risk than any other. Finally, it is imperative to recognize what a massive amount of research does show: That not wearing sunscreen, as well as prolonged sun exposure, are both related to lots of serious skin problems.

(Sources for the above: Aquatic Toxicology, November 2008, pages 182–187; American Journal of Clinical Nutrition, August 2008, pages 570S–577S; Environmental Health Perspectives, July 2008, pages 893–897; Journal of the American Academy of Dermatology, May 2008, pages S155–S159; Journal of the European Academy of Dermatology and Venereology, April 2008, pages 456–461; International Journal of Andrology, April 2008, pages 144–151; Toxicology, July 2007, pages 140–148; Advanced Drug Delivery Reviews, July 2007, pages 522–530; Critical Reviews in Toxicology, March 2007, pages 251–277; 2007 CIR Compendium, Cosmetic Ingredient Review, 2007, pages 37–38; www.cosmeticinfo.org; Current Drug Delivery, October 2006, pages 405–415; Toxicology In Vitri, April 2006, 301–307; Toxicological Sciences, April 2006, pages 349–361; Skin Pharmacology and Physiology, July-August 2005, pages 170–174; Toxicology, December 2004, pages 123–130; Journal of Controlled Release, June 2002, pages 225–233; November 2002, pages S131–S155; http://ec.europa.eu/health/ph_risk/committees/sccp/docshtml/sccp_out145_en.htm; and Encyclopedia of Pharmaceutical Technology, Second Edition, Volume 1, page 519.)