Lignin shown to enhance sunscreen effectiveness
This could turn out to be quite the discovery given that there have been safety concerns over the cosmetics application of the wood derivative.
Lignin is a complex organic polymer found in the cell walls of plants, and is already known to be a good UV-absorber and a broad-spectrum sun blocker.
Over 50 million tons of it 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 Technology, Guangzhou, and Shiping Zhu from McMaster University, Ontario, to investigate their sunscreen performance.
To do this they added 10% by weight of lignin into a moisturising cream initially and found that it actually outperformed a commercial SPF-15 sunscreen in blocking the transmittance of UVA light, when it came to sun protection factor.
Then they added the same amount (10wt%) into a commercial SPF-15 sunscreen and found that it dramatically enhanced its performance, giving an SPF value as high as 89.58, clearly surpassing a commercial SPF-50 lotion.
The study was published in the journal Green Chemistry, and this level of enhancement was higher than expected, according to Zhu.
Zhu explains that the effectiveness of the lignin as a sunscreen additive is two-fold.
“First, lignin contains UV-absorbing functional groups such as phenols, ketones and other chromophores,” he says.
“Second, lignin is an excellent natural antioxidant and it can protect other active ingredients in sunscreens.”
As a bonus to the study, the team also found that 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,” she says.
The researchers plan to investigate this synergistic effect as well as screen different lignin products to obtain the best possible sunscreen performance.