Titanium dioxide and zinc oxide nanoparticles in sunscreens: focus on their safety and effectiveness

Abstract

Sunscreens are used to provide protection against adverse effects of ultraviolet (UV)B (290-320 nm) and UVA (320-400 nm) radiation. According to the United States Food and Drug Administration, the protection factor against UVA should be at least one-third of the overall sun protection factor. Titanium dioxide (TiO2) and zinc oxide (ZnO) minerals are frequently employed in sunscreens as inorganic physical sun blockers. As TiO2 is more effective in UVB and ZnO in the UVA range, the combination of these particles assures a broad-band UV protection. However, to solve the cosmetic drawback of these opaque sunscreens, microsized TiO2 and ZnO have been increasingly replaced by TiO2 and ZnO nanoparticles (NPs) (<100 nm). This review focuses on significant effects on the UV attenuation of sunscreens when microsized TiO2 and ZnO particles are replaced by NPs and evaluates physicochemical aspects that affect effectiveness and safety of NP sunscreens. With the use of TiO2 and ZnO NPs, the undesired opaqueness disappears but the required balance between UVA and UVB protection can be altered. Utilization of mixtures of micro- and nanosized ZnO dispersions and nanosized TiO2 particles may improve this situation. Skin exposure to NP-containing sunscreens leads to incorporation of TiO2 and ZnO NPs in the stratum corneum, which can alter specific NP attenuation properties due to particle-particle, particle-skin, and skin-particle-light physicochemical interactions. Both sunscreen NPs induce (photo)cyto- and genotoxicity and have been sporadically observed in viable skin layers especially in case of long-term exposures and ZnO. Photocatalytic effects, the highest for anatase TiO2, cannot be completely prevented by coating of the particles, but silica-based coatings are most effective. Caution should still be exercised when new sunscreens are developed and research that includes sunscreen NP stabilization, chronic exposures, and reduction of NPs' free-radical production should receive full attention.

Nanoparticles and Bacteria

“…This manuscript supports the observation that actually the antibacterial features may not be a direct result of the presence of TiO 2 but a consequence of ROS interacting with the membrane of bacteria. A better knowledge of the interactions between TiO 2 (or ZnO), electromagnetic radiation, and water is mandatory in understanding the chemical processes and risks implied by the use of sunscreens and/or cosmetics based on oxide semiconductors [28]. Recent studies suggest that sonication can replace the electromagnetic radiation in the generation of ROS in TiO 2 [17,29].…”

“…The large absorbance of TiO 2 in UV is widely recognized and documented. Micron sized TiO 2 particles are efficient in blocking UVB type of radiation while micron sized ZnO nanoparticles are preferentially absorbing in UVA-1 domain [28]. Nevertheless, as the UV radiation is absorbed, electron-hole pairs are generated and ROS production is ignited in both ZnO and TiO2 particles.…”

Evaluation of Recovery From Acute Lung Injury Induced by Intratracheal Instillation of Zinc Oxide Nanoparticles

“…Metal nanoparticles such as silver, titanium, zinc, and aluminum are widely used. For example, zinc nanoparticles (Zn-NPs) and titanium nanoparticles (Ti-NPs) are currently used in sunscreen cosmetics for the prevention of ultraviolet (UV) radiation-induced dermal diseases, including carcinoma and burns (Monteiro-Riviere et al, 2011, Smijs andPavel, 2011, Nohynek andDufour, 2012). However, previous studies have shown that metal nanoparticles induced DNA damage and oxidative stress in keratinocytes (Shukla et al, 2011), hepatoma cells (Kim et al, 2009) and lung epithelial cells (Limbach et al, 2007).…”

Effect of Nanoparticles on Biodiversity of Soil and Water Microorganism Community

“…Moreover, these are also being used in solar-cell, photovoltaics, piezo-electronic devices [7,8]. Amongst several metal oxides, zinc oxide, and titanium oxide are very commonly used in sunscreens and cosmetics [9][10][11][12][13]. With the increasing production and use of nanomaterials, their inevitable release to the environment increases.…”