Sunscreens Causing Cancer? The Facts

Skin cancer is the most common form of cancer in the United States and continues to rise in incidence and mortality each year.¹ It is common knowledge that UV light plays a major role in the development of skin cancer.^2,3 Studies have long demonstrated that using sunscreen on a daily basis can help prevent the development of skin cancer, premature aging, and exacerbation of photodermatoses.^4-7 Although there are several photoprotective measures available, sunscreen remains the most popular and widely used among patients.⁸ Sunscreens that are on the market today contain either organic or inorganic UV filters or a combination of both based on their chemical composition and photoprotection mechanisms.⁹ Concerns about these ingredients causing cancer have created confusion among consumers. I will attempt to clarify these concerns by critically analyzing available evidence-based data on sunscreen use so that as dermatology residents we will be more knowledgeable about sunscreen safety topics and will be able to provide accurate and up-to-date information to our patients.

Organic UV Filters

Organic UV filters are classified as aromatic compounds that provide photoprotection by absorbing UV light.¹⁰ Aside from the photoallergic potential of organic UV filters, controversy has arisen in response to studies reporting their possible hormone disruptive effects.^11-18 Although there are several US Food and Drug Administration (FDA)–approved organic UV filters in use today, one of the most commonly manufactured and controversial agents is oxybenzone.¹⁰ Claims regarding the estrogenic and antiandrogenic effects of oxybenzone have been investigated with results refuting the claims or concluding that more sensitive studies are needed to determine if these organic ingredients pose such risks.^10,19,20 One study demonstrated that nearly 300 years of daily sunscreen application would be needed to reach similar exposure levels of oxybenzone used and described in prior animal studies.²¹ Additionally, most of the studied adverse effects of UV filters have been evaluated based on oral exposure rather than actual dermal application.¹¹ Although these compounds are absorbed systemically, studies have reported that the amounts are insignificant and noncumulative in the body.^10,22-24 Furthermore, the binding affinity of oxybenzone for estrogen receptors has been shown to be much weaker and near insignificant compared to estrogen and estradiol.^24,25 Although numerous important studies examining systemic absorption have not shown a clinically significant disruption of hormonal homeostasis or acute toxicity in humans by organic UV filters, further studies are needed.

Inorganic UV Filters

Used as the main active ingredients in sunscreen for decades, titanium dioxide (TiO₂) and zinc oxide (ZnO) compounds generally are more photostable and less photoallergic than their organic counterparts.¹⁰ In recent years, the safety of these long-used photoprotectors has been questioned because of the development of nanoparticle (<100 nm) formulas that are less opaque on application. Although this formula provides a thin, transparent, and cosmetically appealing medium, there is concern that the metal oxides penetrate the skin and cause local and systemic toxicities.^26-28 Several recent scientific studies have shown no percutaneous permeation of these particles in normal adult human skin and reported no causal damage to mammalian cells.^10,29-31 Although skin penetration of TiO₂ and ZnO has been described as insignificant, focus has shifted to health risks associated with inhaling TiO₂ through the use of spray or powder products following statements made by the International Agency for Research on Cancer in 2006.³² Several studies investigating increased health risks, specifically lung cancer, in factory workers who were subjected to TiO₂ and ZnO inhalation concluded that exposure was unlikely to pose substantial health risks or subchronic toxicity.^33,34 Despite a relatively strong safety profile, a major concern of using these metal oxides as UV filters has been potential free radical formation.^35-39 For this reason, the Scientific Committee on Emerging and Newly Identified Health Risks extensively researched and delivered opinions on the use of TiO₂ and ZnO in cosmetics, concluding that topical application of either compound does not result in toxicity or other adverse effects.^30,40-42 Additionally, an effort has been made by manufacturers to encapsulate nanoparticles with magnesium and other materials to quench the reactive oxygen species along with the human body’s own antioxidant defense system.¹⁰ In summary, it appears that the current weight of scientific evidence suggests that percutaneous absorption and toxicity by UV filters in humans may be overestimated and that the use of nanoparticles in sunscreens poses no or negligible potential risks to human health.^43,44