A study published earlier this month in Cosmetics found that the combination of mesoporous silica and titanium dioxide resulted in a higher sun protectant factor and greater photostability than the UV filter alone.
The authors write, “improving sunscreen formulations to provide a photostable profile associated with a broad-spectrum protection has become an utmost relevant issue in the cosmetic science and dermocosmetics in general.”
Inorganic UV filters such as titanium dioxide and zinc oxide are often chosen for children and individuals with sensitive skin or allergies because of their low irritation and photosensitization rates. The authors of this study tested whether a substrate such as mesoporous silica may increase the protective effects of titanium dioxide.
Because lips are more sensitive to UV radiation than skin, they formulated a sunscreen lipstick for the experiment. The authors write, “...the application of lipstick sunscreens is of great importance and expected to provide protection of this particular area against sunburn and photoaging, among other unfavorable responses to unprotected UV exposure.”
Researchers created several lipsticks including a base control sample; one with only mesoporous silica as the additive; one with only titanium dioxide; and one with titanium dioxide encapsulated into mesoporous silica. The lipsticks with titanium dioxide and silica-titanium dioxide combination contained 10% active ingredients.
Photoprotection efficacy (the SPF) was tested using a diffuse reflectance spectrophotometer with an integration sphere. Photostability was evaluated using a solar simulator with xenon lamp, optical filter and infrared filter. SPF was analyzed prior to and after irradiation.
According to the authors, “photostability to UV radiation is an important parameter since a sensitive UV-filtering molecule could degrade and induce photoallergy and phototoxicity.”
The lipstick with titanium dioxide encapsulated into mesoporous silica showed greater photostability and higher SPF than the lipstick with titanium dioxide alone. Titanium dioxide alone was not able to achieve broad-spectrum sun protection; however, the encapsulated formula with silica did. The SPF value was greater than 15 and the critical wavelength above 370 nanometers.
The researchers write that the increased SPF in the mesoporous silica-titanium dioxide lipstick may suggest a synergistic effect between mesoporous silica and titanium dioxide.
Regarding photostability, the lipstick containing the mesoporous silica and titanium dioxide did not have a statistically significant change in SPF after irradiation via the solar simulator. This suggests a photostable product, the authors write.
“During recent years, there has been growing interest in the development of safer and more effective sunscreens using several strategies...We suggest that TiO2 + mesoporous silica (SBA-15) could be considered a broad-spectrum ingredient for innovative sunscreens in the future, particularly for photoprotection of the lips.”
2023 10(2): 46 https://doi.org/10.3390/cosmetics10020046
“In Vitro Photoprotection and Functional Photostability of Sunscreen Lipsticks Containing Inorganic Active Compounds.”
Authors: Marcelino, P.S.D., et al.