Lignin boosts sunscreen performance

Scientists in Canada and China have shown that the effectiveness of commercial sunscreens can be enhanced by the addition of lignin and, as an unprecedented bonus; sunlight exposure may help them work even better.

Lignin, a complex organic polymer found in the cell walls of plants, is already known to be a good UV-absorber and a broad-spectrum sun blocker. Over 50 million tons of lignin is produced industrially each year, but it has never been used in sunscreens before due to safety concerns. However, recent studies have shown that certain types of industrial lignin are safe, and this inspired Xueqing Qiu from South China University of Technnology, Guangzhou, and Shiping Zhu from McMaster University, Ontario, to investigate their sunscreen performance.

Adding 10wt% lignin into moisturising creams gave sunscreens with sun protection factors (SPF) up to 5.72, outperforming a commercial SPF-15 sunscreen in blocking the transmittance of UVA light. Adding 10wt% lignin into a commercial SPF-15 sunscreen dramatically enhanced its performance, giving an SPF value as high as 89.58, clearly surpassing a commercial SPF-50 lotion. This level of enhancement was higher than expected, according to Zhu.

The effectiveness of the lignin as a sunscreen additive is two-fold, explains Zhu. ‘First, lignin contains UV-absorbing functional groups such as phenols, ketones and other chromophores. Second, lignin is an excellent natural antioxidant and it can protect other active ingredients in sunscreens’.

Surprisingly, the performances of the sunscreens were found to improve after UV irradiation, meaning that the sunscreens could potentially improve after sun exposure. This unusual effect is the most intriguing aspect of this work according to Clara Piccirillo, an expert in materials science from the Portuguese Catholic University in Porto; ‘Obviously it is a very positive thing, as it means that the sunscreen would be even more effective; I think, however, that more studies should be done to understand better how and why this happens.’

The researchers plan to investigate this synergistic effect as well as screen different lignin products to obtain the best possible sunscreen performance.