This case study reports a multi-technique characterization of two commercially available sunscreens—one mineral-based (TiO₂/ZnO) and one chemical-based—motivated by real-world differences in skin irritation. Volatile organic compounds in the chemical sunscreen were identified by GC–MS/TOF-MS both immediately after dispensing and after two hours of sunlight exposure; the post-exposure chromatogram showed a shifted chemical profile and new peaks consistent with UV-driven reactions/photodegradation products. Trace metals were quantified by ICP-MS across a broad elemental panel; both sunscreens contained detectable metals, but all were measured at concentrations below topical toxicity thresholds. Finally, SEM-EDS was used to examine mineral sunscreen particulates, revealing two distinct nanoparticle morphologies and confirming (via elemental mapping and spectra) a relatively uniform TiO₂ distribution alongside Zn-rich, rod-like agglomerates that likely contribute to visible “white cast.”
What’s Really in Our Sunscreens?
What changes in a sunscreen after a couple of hours in the sun, and what’s actually in the bottle? We compared a mineral sunscreen (zinc oxide and titanium dioxide) with a chemical sunscreen using GC-MS, ICP-MS and SEM-EDS to track how the chemical formula changed under sunlight, test both products for trace heavy metals, and image the nanoparticles in the mineral formula. One finding helps explain why mineral sunscreens leave a white cast.