Mitigating the skin irritation potential of mixtures of anionic and non-ionic surfactants by incorporating low-toxicity silica nanoparticles

[Display omitted] •The non-ionic surfactant has the lowest risk of skin irritation.•Non-ionic/anionic combinations reduced skin irritability by 24–67 % over the single anionic surfactant.•Silica nanoparticles (NP) increased the skin irritation potential of single surfactants.•The formulation stability of surfactant mixtures improves with the addition of NP.•The irritation potential of anionic/non-ionic mixtures of surfactants can be further reduced by adding silica NPs. There has been a notable upswing in the adoption of product formulations based on nanotechnology within the cosmetics industry. By using nanocarriers, such as solid or micellar nanoparticles, the quality and performance of cosmetics can be improved, allowing for better transport of bioactive components into the skin. However, it is important to note that the interaction between these compounds may lead to skin irritation. To mitigate skin irritability, nano-formulation strategies should be implemented in cosmetics. A proof-of-concept study was therefore conducted to investigate if low-toxicity nanoparticles (silica) could be used in combination with a mixture of anionic surfactants and a low-irritant cosurfactant (non-ionic) to develop safer cosmetic formulations that reduce skin damage. The skin irritation potential of the formulations was assessed in vitro using the well-known Zein method. As anticipated, non-ionic surfactants pose the lowest risk for skin irritation. When compared to single anionic surfactants, non-ionic/anionic mixtures were found to decrease skin irritability by 24–67 %. However, when silica nanoparticles (NPs) were added to single surfactants, the potential for skin irritation increased, particularly when the anionic surfactant molecules were arranged in a spherical core-shell structure around the surface of the NPs. On the other hand, incorporating NPs in surfactant mixtures enhanced their formulation stability. While all three-component formulations were found to decrease skin irritability, those that formed spherical core-shell structures demonstrated the most significant reduction, likely related to a reduction in charge density caused by the non-ionic surfactant which may decrease protein solubilisation. Therefore, the inclusion of silica NPs can potentially result in a further reduction of the skin irritation potential caused by mixtures of anionic and non-ionic surfactants.