Sunscreen fact and fiction: What the science says

This summary is based on peer-reviewed literature and current clinical guidelines, cited below.

Background

Sunscreen counseling is one of the most frequent OTC conversations pharmacists have, yet it is also one of the most muddled by online misinformation about “chemical” versus “mineral” filters, hormone disruption, and SPF math. Ultraviolet B (UVB) radiation causes direct DNA damage linked to keratinocyte carcinomas, while longer-wavelength UVA penetrates deeper and drives photoaging and oxidative skin damage; adequate photoprotection requires blocking both.¹

Clinical Considerations

SPF, Broad-Spectrum Labeling, and Application Technique

SPF is not a linear scale: SPF 15 filters approximately 93% of UVB radiation, SPF 30 filters about 97%, and SPF 50 roughly 98% — the marginal gain shrinks quickly above SPF 30.¹ A “broad spectrum” label is the FDA designation confirming a product meets minimum UVA protection standards in addition to its SPF (UVB) rating, and it should be considered non-negotiable regardless of SPF number.¹ The dominant real-world failure point is under-application: most users apply well below the tested reference dose of 2 mg/cm², which substantially undercuts the labeled SPF. Counsel patients to use a generous, visible layer and to reapply at least every two hours, or immediately after swimming or heavy sweating.¹

Mineral vs. Chemical Filters: Systemic Absorption

Chemical (organic) filters such as avobenzone, oxybenzone, octocrylene, homosalate, octisalate, and octinoxate absorb UV energy, while mineral (inorganic) filters — zinc oxide and titanium dioxide — primarily reflect and scatter it. In an FDA-sponsored randomized clinical trial, all six tested chemical active ingredients were systemically absorbed at plasma concentrations exceeding the agency’s 0.5 ng/mL threshold for waiving additional nonclinical toxicology testing, in some cases after a single application.³ Critically, the trial authors emphasized that these findings do not indicate patients should avoid sunscreen — systemic absorption is not the same as demonstrated harm, and no clinical outcome data currently link these plasma levels to adverse effects.³ This is useful, precise language for counseling patients who raise “chemical sunscreen” safety concerns: absorption has been measured, but a hormonal or carcinogenic effect at these concentrations has not been established. Mineral formulations remain a reasonable preference for patients who are pregnant, are counseling for use in young children, or have sensitive or reactive skin.

Skin of Color and Risk-Based Counseling

Skin cancer is less common in patients with darker skin tones but is frequently diagnosed at a more advanced stage, contributing to worse outcomes; this is attributable in part to a persistent public and clinical assumption that photoprotection counseling is unnecessary in this population.² Pharmacists should extend sunscreen and sun-protective-behavior counseling — and skin self-examination education — to all patients regardless of skin tone, not only those at classically “high-risk” (fair-skinned) phenotypes.²

Vitamin D and Non-Sunscreen Measures

Regular sunscreen use blocks only a fraction of incidental UVB exposure in practice, and clinically meaningful vitamin D deficiency attributable to sunscreen use alone is not well supported; patients with documented deficiency are better served by dietary sources or supplementation than by reducing photoprotection. Sunscreen should also be framed as one layer of a broader regimen that includes shade, sun-protective clothing, and UV-blocking eyewear, since no sunscreen blocks 100% of UV radiation.¹

Bottom Line for Pharmacists

Recommend a broad-spectrum product of at least SPF 30, applied generously and reapplied every two hours. Mineral filters are a sound alternative for patients concerned about systemic absorption, pregnancy, pediatric use, or sensitive skin, but both filter classes are effective when used correctly — the best sunscreen is the one a patient will actually apply consistently. Extend this counseling to every patient, regardless of skin tone, and reinforce that sunscreen is one part of a layered sun-protection strategy, not a substitute for shade and protective clothing.

References

1. Li H, Colantonio S, Dawson A, Lin X, Beecker J. Sunscreen application, safety, and sun protection: the evidence. J Cutan Med Surg. 2019;23(4):357-369. https://doi.org/10.1177/1203475419856611
2. Agbai ON, Buster K, Sanchez M, et al. Skin cancer and photoprotection in people of color: a review and recommendations for physicians and the public. J Am Acad Dermatol. 2014;70(4):748-762. https://doi.org/10.1016/j.jaad.2013.11.038
3. Matta MK, Florian J, Zusterzeel R, et al. Effect of sunscreen application on plasma concentration of sunscreen active ingredients: a randomized clinical trial. JAMA. 2020;323(3):256-267. https://doi.org/10.1001/jama.2019.20747