Recent developments in nanomaterials in personal care products

To fully understand potential consumer risks, exposure studies must be considered in parallel with toxicity studies. Exposure helps estimate the dose of nanomaterials that a human organ might receive under real conditions. Common challenges in exposure assessment arise from the dynamic shape, size, and aggregation of nanoparticles with other cosmetic ingredients. In order to meet the requirements of experimental data, some exposure models of nanomaterials need to be established. These models include the Stoffenmanager Nano model (qualitative exposure estimation), NanoSafer and ConsExpo nano models (quantitative exposure estimation).

However, according to the European Regulation on Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) in the European Union, current exposure models cannot be compared with experimental measurements because they cannot account for this dynamic aggregation/aggregation and shape change.

There is a long-standing debate about what specific measures might be required for a thorough exposure assessment. For large particles, particle mass measurements are useful, but nanomaterials contribute little to the mass relative to rough materials. Nor can particle mass explain the structural and functional properties of nanomaterials. The researchers suggest a combination of measurement methods to more accurately assess the exposure of nanomaterials - suggested measurement characteristics include shape, surface area, surface chemistry, surface charge, size, chemical composition, crystal structure, porosity, and agglomeration state. REACH also extensively lists the nano-specific data required for a comprehensive exposure assessment of nanomaterials.

03 Toxicity

Consumer exposure to personal care products mainly occurs at the product use stage and is associated with the greatest risk of exposure to nanomaterials. Toxicity assessment using in vitro and in vivo tests usually follows recommended guidelines set by international organizations such as the Organization for Economic Cooperation and Development (OECD) or the International Organization for Standardization (ISO). Although data in vitro and in animals provide valuable predictions of the extent of harm and potential mechanisms of action, these studies are not always correct for predicting biological effects in humans. Since human data for Ag, TiO2, and ZnO nanoparticles are available, we will focus on reviewing toxicological data from human exposure studies.

Human skin exposure data for the presence of Ag, TiO2 and ZnO nanoparticles in textiles and sunscreen products. Studies using wound dressings and textiles containing Ag nanoparticles have shown no change in serum Ag levels and no discomfort or histopathological changes in the skin after about a week of direct contact. For physical sunscreens, the active ingredient is usually a mixture of TiO2 and ZnO.

In a study by Tan et al., volunteers applied a sunscreen containing 8%TiO2 twice daily for 9-31 days. No obvious trauma, rash or adverse reactions were observed. Skin exposed to titanium concentrations (0-4 µg/g) and control tissues (0-2 µg/g), no correlation was found between exposure duration and concentration. When the sunscreen combined with TiO2 nanoparticles and ZnO nanoparticles penetrated the epidermis with a higher concentration of zinc (1.25 -- 2.66µmol/ g) than titanium, titanium was not detected.

Two studies by Gulson et al. examined the efficiency of zinc absorption in the skin by using the stable isotope Zn68, which contains a relatively low natural abundance. Fourteen healthy volunteers were treated with a dose containing 4.3 mg/cm2