Titanium DioxidevsZinc Oxide

Titanium dioxide (TiO2) absorbs, scatters, and reflects UV radiation through its semiconductor properties and high refractive index. It provides excellent UVB protection (280–320 nm) and short-wave UVA (UVA-II, 320–340 nm) protection, but exhibits a band-gap that limits efficacy against long-wave UVA (UVA-I, 340–400 nm). This spectral gap is why titanium dioxide is typically combined with zinc oxide in mineral sunscreens for comprehensive coverage. Like zinc oxide, titanium dioxide is photostable—it does not degrade or isomerize with UV exposure, unlike some organic filters. Micronized and nano forms reduce white cast while maintaining efficacy. Titanium dioxide particles remain on the skin surface and do not penetrate intact stratum corneum. Uncoated nano TiO2 can generate reactive oxygen species (ROS) under UV; surface coatings (silica, alumina) mitigate this. Clinically, it is well-tolerated and non-comedogenic.

Zinc oxide particles sit on the skin surface and primarily scatter and reflect UV radiation across the full UVA (320–400 nm) and UVB (280–320 nm) spectrum via Rayleigh and Mie scattering. At nano scale, zinc oxide also absorbs UV photons and undergoes semiconductor band-gap excitation, converting UV energy to heat—a mechanism similar to organic chemical filters. It provides the broadest single-ingredient UV coverage available. Beyond photoprotection, zinc oxide exerts anti-inflammatory effects by inhibiting NF-κB activation, reducing pro-inflammatory cytokine release (TNF-α, IL-6), and modulating Toll-like receptor signaling. It supports barrier repair by promoting occludin and zonula occludens-1 expression in tight junctions. Zinc ions have mild antimicrobial activity against Staphylococcus aureus and Candida species. These properties underlie its use in diaper rash creams, wound care, and post-procedure skincare. Zinc oxide does not penetrate intact stratum corneum when formulated as micronized or nano particles.