The European Union (EU) Observatory for Nanomaterials (EUON) announced on May 20, 2020, that a recent study has analyzed existing research on whether nanomaterials used in consumer products and at workplaces are absorbed through the skin. The study was commissioned by EUON and carried out by the RPA consortium of Triskelion and the Dutch National Institute for Public Health and the Environment (RIVM). According to EUON, the study found that the lack of standardized, validated methods and the use of varying testing protocols make it difficult to compare results and evaluate whether nanomaterials can penetrate the skin. EUON states that “[b]ased on the findings, nanomaterials rarely absorb through intact skin, except for silver that is likely to partly penetrate in ionic form. Silver is used for its anti-bacterial properties in textiles and can be found in other consumer products such as pharmaceuticals and cosmetics.” Some of the analyzed studies suggest that absorption through damaged skin is higher than through intact skin. EUON notes that a key recommendation for any new studies that aim to provide proof of skin absorption is to perform them using tests performed on tissue in external environments with minimal alterations to natural conditions (ex vivo), comparable to the Organization for Economic Cooperation and Development (OECD) Test Guideline 428, with human or porcine skin. EUON states that rodent skin should not be used due to differences in skin characteristics between rodents and humans.
The study covered experimental data, including tests performed inside the bodies of living organisms (in vivo) and ex vivo studies. It looked at factors associated with test methodology that can affect absorption through the skin, for example: exposure conditions; different experimental set-ups; and methods. The effects of the characteristics of nanomaterials on skin absorption, including particle size and surface charge, were also analyzed. According to EUON, in addition to compiling relevant studies, the study looked at test guidelines and whether the results are available in a structured way, for example, following OECD harmonized templates.