When formulating sunscreens, getting the emollient wrong can lead to uneven UV protection and white casting on the skin. Nobody wants that ashy, uneven look or a sun cream that isn’t reliable. So how can you make sure that your sunscreen is smooth and absorbable, with no residue on the skin? It all comes down to the emollient.
Emollients play a crucial role in sunscreens, having a more technical or sensorial role. Apart from providing emollience to the formulation, they impact the skin feel. Chemically, they solubilize organic filters or disperse mineral UV filters. There is a trend to use more mineral filters as brands turn to these filters as a way to formulate their sunscreens in a more natural way. However, working with mineral UV filters such as zinc oxide or titanium dioxide can be challenging, so choosing the right emollient is essential to get the desired qualities in your final product.
Mineral UV filters are particles and powders that you need to load into your formulation. They need to be dispersed in the emollient phase, often demanding high amounts of powder in the formulation. Minerals add a lot of viscosity, making formulations thicker and harder to handle. There is a risk that UV filters agglomerate. This would cause uneven sun protection and white casting on the skin. Such irregular protection would mean some areas are left unprotected, meaning the sun cream would fail to do its only job. So how can you prevent this from happening?
A number of consumer reports point to the fact that consumers would like to have light, fluid formulations that are easy to spread on the skin. Otherwise, they won’t use enough sunscreen. The key to smooth formulations is to avoid agglomeration by using the right emollient to disperse the UV filter in an even way.
When choosing an emollient, it’s important to select one that also fully wets the surface of the particles, causing no agglomeration. The emollient needs to create low viscosity dispersions at high levels of SPF filter. Also, if you choose an efficient emollient, you can use less of it, leaving room for more water in the formulations – leading to a lighter formulation.
At AAK, we have evaluated different emollients that are typically used in suncare products. In our lab, we have focused on some simple, but very efficient test methods that you could use in your own lab to help you make the right selection when formulating your sunscreen.
Our main experiments have focused on viscosity as a key measurement. We looked at the global suncare market and identified five different solutions: Caprylic/ Capric Triglyceride, C12-15 Alkyl Benzoate, Coco-caprylate/Caprate, Lipex SheaSolve and Dicaprylyl Carbonate. In our lab, we conducted some experiments to show how different emollients behave when loaded with zinc oxide. For example, we loaded 40% coated zinc oxide into the different emollients and compared the results that showed a big difference in viscosity between the emollients. See the results yourself in this webinar (insert link). If you want to generate low viscous dispersions, you need to turn to the more polar, low viscous esters, such as Lipex SheaSolve.
In another viscosity test, we used an ISO flow cup to measure viscosity. The results of the experiment presented in this webinar show a big difference in viscosity depending on which emollient is being used when used in a 20% zinc oxide dispersion. Lipex SheaSolve shows nice fluid dispersion, as it moves quickly through the funnel. C12-C15 Alkyl Benzoate took a longer time to pass through, while Caprylic/Capric Triglyceride generated very thick, viscous dispersions. Even if you don’t have an ISO cup in your lab, you can use a basic funnel that you may have at hand to do similar experiments.
Predicting the viscosity of a final dispersion can’t be done just by looking at the viscosity of the pure emollient. To understand the microstructure of these dispersions, we made use of microscopy. In the results (insert link), you can see how C12-C15 Alkyl Benzoate, for example, didn’t disperse the mineral UV filter so well, and Caprylic/Capric Triglyceride caused even more agglomerates. Lipex SheaSolve dispersed the filter evenly across the formulation. So, the choice of emollient does matter and impacts how well the filter is being wetted throughout the sample.
Another simple test you could do in your lab is a skin test. Agglomeration may lead to a white casting formed when applied to the skin. To test this whitening effect in our lab, we applied dispersions to the skin. We measured two squares marked on the skin, applied the same amount of emollient to this area and with the same motion. The result was that the choice of emollient does impact how much whitening you get on the skin. Lipex SheaSolve is a better choice if you want to avoid agglomeration and whitening on the skin when compared to the other emollients tested.
As the nature of mineral UV filters makes them prone to agglomeration and viscosity, it’s essential to use an effective emollient. The higher the SPF value you want to achieve, the higher the amount of mineral filter to be dispersed, and the higher the chances that the final formulation will be thick and with poor sensorial benefits for consumers. By choosing an effective emollient to disperse the UV filter, you can maintain low viscosity and prevent particle agglomeration and skin casting. In experiments, Lipex SheaSolve, a polar, low viscous ester derived from shea butter, serves as an effective, natural solution for dispersing UV filters. By choosing the right emollient you can overcome the challenges when formulating mineral sunscreens. You can make sure your end product has that smooth feel on the skin and even sun protection you can trust.
Do you want to learn more about choosing the right emollient for mineral suncare formulations?