Sunscreen is a cornerstone of skin cancer prevention. The first commercial sunscreen was developed nearly 100 years ago,1 yet questions and concerns about the safety of these essential topical photoprotective agents continue to occupy our minds. This article serves as an update on some of the big sunscreen questions, as informed by the available evidence.
Are sunscreens safe?
The story of sunscreen regulation in the United States is long and dry. The major pain point is that sunscreens are regulated by the US Food and Drug Administration (FDA) as over-the-counter drugs rather than cosmetics (as in Europe).2 Regulatory hurdles created a situation wherein no new active sunscreen ingredient has been approved by the FDA since 1999, except ecamsule for use in one product line. There is hope that changes enacted under the CARES Act will streamline and expedite the sunscreen approval process in the future.3
Amid the ongoing regulatory slog, the FDA became interested in learning more about sunscreen safety. Specifically, they sought to determine the GRASE (generally regarded as safe and effective) status of the active ingredients in sunscreens. In 2019, only the inorganic (physical/mineral) UV filters zinc oxide and titanium dioxide were considered GRASE.4 Trolamine salicylate and para-aminobenzoic acid were not GRASE, but they currently are not used in sunscreens in the United States. For all the remaining organic (chemical) filters, additional safety data were required to establish GRASE status.4 In 2024, the situation remains largely unchanged. Industry is working with the FDA on testing requirements.5
Why the focus on safety? After all, sunscreens have been used widely for decades without any major safety signals; their only well-established adverse effects are contact dermatitis and staining of clothing.6 Although preclinical studies raised concerns that chemical sunscreens could be associated with endocrine, reproductive, and neurologic toxicities, to date there are no high-quality human studies demonstrating negative effects.7,8
However, exposure patterns have evolved. Sunscreen is recommended to be applied (and reapplied) daily. Also, chemical UV filters are used in many nonsunscreen products such as cosmetics, shampoos, fragrances, and plastics. In the United States, exposure to chemical sunscreens is ubiquitous; according to data from the National Health and Nutrition Examination Survey 2003-2004, oxybenzone was detected in 97% of more than 2500 urine samples, implying systemic absorption but not harm.9
The FDA confirmed the implication of systemic absorption via 2 maximal usage trials published in 2019 and 2020.10,11 In both studies, several chemical sunscreens were applied at the recommended density of 2 mg/cm2 to 75% of the body surface area multiple times over 4 days. For all tested organic UV filters, blood levels exceeded the predetermined FDA cutoff (0.5 ng/mL), even after one application.10,11 What’s the takeaway? Simply that the FDA now requires additional safety data for chemical sunscreen filters5; the findings in no way imply any associated harm. Two potential mitigating factors are that no one applies sunscreen at 2 mg/cm2, and the FDA’s blood level cutoff was a general estimate not specific to sunscreens.4,12
Nevertheless, a good long-term safety record for sunscreens does not negate the need for enhanced safety data when there is clear evidence of systemic absorption. In the meantime, concerned patients should be counseled that the physical/mineral sunscreens containing zinc oxide and titanium dioxide are considered GRASE by the FDA; even in nanoparticle form, they generally have not been found to penetrate beneath the stratum corneum.7,13