Support for the Safe Use of Zinc Oxide Nanoparticle Sunscreens: Lack of Skin Penetration or Cellular Toxicity after Repeated Application in Volunteers

Abstract

Zinc oxide is a widely used broad-spectrum sunscreen, but concerns have been raised about the safety of its nanoparticle (NP) form. We studied the safety of repeated application of agglomerated zinc oxide (ZnO) NPs applied to human volunteers over 5 days by assessing the skin penetration of intact ZnO-NPs and zinc ions and measuring local skin toxicity. Multiphoton tomography with fluorescence lifetime imaging microscopy was used to directly visualize ZnO-NP skin penetration and viable epidermal metabolic changes in human volunteers. The fate of ZnO-NPs was also characterized in excised human skin in vitro. ZnO-NPs accumulated on the skin surface and within the skin furrows but did not enter or cause cellular toxicity in the viable epidermis. Zinc ion concentrations in the viable epidermis of excised human skin were slightly elevated. In conclusion, repeated application of ZnO-NPs to the skin, as used in global sunscreen products, appears to be safe, with no evidence of ZnO-NP penetration into the viable epidermis nor toxicity in the underlying viable epidermis. It was associated with the release and penetration of zinc ions into the skin, but this did not appear to cause local toxicity.

A minimally invasive clinical model to test sunscreen toxicity based on oxidative stress levels using microbiopsy and confocal microscopy – a proof of concept study

“…The study concluded, however, that the penetration was concentrated mainly in the skin furrows and in support of Lin et al [15] also showed ZnO-NP exposure did not cause any cellular metabolic changes [14]. Mohammed et al showed the lack of skin penetration and cellular toxicity after repeated use of ZnO nanoparticles in volunteers [17,18].…”

“…Likewise, the biological material interacting with the nanoparticle surface, that is corona, will be completely different from that in cell culture [19]. Thirdly, there is a growing body of evidence showing that the stratified structure of skin forms an effective barrier against these nanoparticles in penetrating into deeper structures [10,17,18]. Because of the presence of the barrier and stratified cell layers, in vivo and 3D reconstructed skin models are the most relevant for cosmeceutical testing.…”

Sunscreen and Suntan Preparations

“…In the brain, the oxidative stress and inflammation reaction were found after ZnO NP exposure and more remarkable changes were identified in aged individual. These kinds of neurotoxicity might due to the destruction of the BBB integrity caused partly by ZnO NPs-induced systemic inflammation [135][136][137][138].…”

A Pharmacological Review of Sunscreen and Suntan Preparations

“…In the brain, the oxidative stress and in lammation reaction were found after ZnO NP exposure and more remarkable changes were identi ied in aged individual. These kinds of neurotoxicity might due to the destruction of the BBB integrity caused partly by ZnO NPs-induced systemic in lammation [142][143][144][145].…”