Evaluation of Indigenous Clays, Ibomvu and Umcako, as Cosmetic Raw Materials: A Physicochemical, Mineralogical, and Toxicological Assessment

Abstract

Indigenous clays are widely used for facial skincare in South Africa, yet their suitability for cosmetic incorporation remains poorly characterised, particularly with respect to elemental safety. This study assessed two traditionally applied clays for acne-prone skin (Umcako and Ibomvu) using a multi-analytical workflow encompassing colorimetry, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), pH measurement, in vitro sun protection factor (SPF) estimation, X-ray fluorescence (XRF), and inductively coupled plasma mass spectrometry (ICP-MS) of clay leachates. XRD showed both materials to be kaolinite-dominated, with higher kaolinite content in Umcako (92.5 wt%) than in Ibomvu (77.3 wt%); SEM revealed characteristic overlapping pseudo-hexagonal platelets, and FT-IR did not indicate prominent organic functional groups under the conditions tested. The clays were mildly acidic (pH 4.23–4.48), aligning with physiological skin pH, but exhibited low photoprotective performance when assessed alone (SPF ≈ 2.5–2.6). Elemental screening identified nutritionally relevant trace minerals but also detected regulated or sensitising metals, with Ibomvu showing elevated bulk Pb (53 ± 12 ppm), Ni (126 ± 71 ppm) and Zn (72 ± 26 ppm), while Umcako contained elevated bulk Cr (460 ± 140 ppm) and Pb (18 ± 6 ppm). Overall, although Umcako and Ibomvu display physicochemical properties compatible with clay-based cosmetic products, their heavy metal burden, together with the potential for dermal exposure highlighted by leachate analysis, indicates that purification, batch-to-batch monitoring and regulatory risk assessment are essential before safe cosmetic use.