Microscopic revelations in sunscreen formulation

Sunscreen formulations are complex and multi-component systems that are based on either organic UV filters, inorganic UV filters, or both. Formulations are most commonly created in emulsion form. Emulsions, as inherently thermodynamically unstable systems by nature, pose a challenge in maintaining stability over time. The overarching objective in the formulation process is to achieve and preserve stability throughout the entire duration of the product’s shelf life. 

Formulators work to address the inherent instability of emulsions, implementing various techniques and strategies to ensure that the sunscreen maintains its efficacy and quality from production through its intended period of use. The pursuit of stability involves a nuanced understanding of the chemical and physical interactions at play, allowing for the development of formulations that withstand environmental factors and the passage of time, ultimately ensuring a reliable and effective sunscreen product for consumers. One key element of predicting stability is using microscopy.

Delving into various facets of microscopy, this article covers critical elements such as timeframes for analysis, slide preparation, incompatibilities, droplet size, and the distinctive appearance of titanium dioxide (TiO2) and zinc oxide (ZnO). With a keen focus on agglomeration challenges posed by these inorganic UV filters, and similarly, crystallisation of organic UV filters, the article also offers guidance to overcome these challenges. As formulators navigate the complexities of sunscreen development, this article provides detailed insights into how microscopy can enhance the understanding of formulation microstructure, offering valuable information beyond what is visible to the naked eye.