Using Small Angle Neutron Scattering (SANS) on the Zoom instrument at ISIS, researchers from De Montfort University and ISIS have investigated the effect of UV filters and preservatives on the microstructure of suncream, with the aim of informing how these additives impact its structure and performance.
In this study, published in RSC Advances, Dr Omar Mansour added some common organic UV filters and preservatives at 'real-life' concentrations to an oil-in-water based sunscreen lotion to create his samples. The UV filters are added for protection from the sun, and preservatives are commonly used to protect the products from microbial contamination.
The microstructures inside the lotion are dictated by surfactant-like interactions; for more information, see our surfactant explainer article. In the untreated lotion, a layered (lamellar) structure was present alongside oil droplets forming in an ellipsoid shape.
When adding the preservatives, there were fewer ellipsoids present, with most of the preservatives present in the lamellar phase. It is therefore likely that the addition of these preservatives has an impact on the texture and feel of the lotion. Adding the UV filters to the lotion also caused disruption to the microstructure, with some filters breaking down the multi-layer lamellar structures.
Combining both preservatives and UV filters, as you would see in a commercial suncream formulation, led to even more complex microstructures forming. These could be caused by the additives interacting with the droplets themselves, or causing changes to the overall system that cause the droplets to interact differently with one another.
“For a long time now, the effect of simple additives such as preservatives on sunscreen lotions was deemed negligible." Explains Dr Mansour; “Our work at ISIS has given us a chance to get a much closer look at these systems for the first time. It turns out that these overlooked effects strongly play a role in determining your lotion's sun protection factor (SPF)."
The full paper can be found at DOI: 10.1039/D1RA00755F