Lignosulfonate is an efficient SPF booster: Application to eco-friendly sunscreen formulations

Sunscreen oil-in-water emulsions containing few ingredients and two EU-authorized organic filters had been developed in an eco-friendly approach. Based on their photostability, spectroscopic features, and the lack of data on toxicity, BEMT (UVA/B range; bis-ethylhexyloxyphenol methoxyphenyl triazine) and DHHB (UVA; diethylamino hydroxybenzoylhexyl benzoate) were selected and incorporated at minimal concentrations to reduce the risk of impact on human health and coastal marine ecosystems. Despite the inconclusive results previously reported, the use of the w-soluble and largely available Na-lignosulfonate (LiS) had been reconsidered with success. Since BEMT and DHHB alone or in combination were not able to higher the sun protection factor (SPF) value at 50, results showed that it becomes possible by supplementing with LiS at 5% (w/w), ensuring stability, antiradical property, and a non-toxicity of the sun emulsion. After defining the range doses for the three components, minimizing concentrations was achieved by experimental design studies using a response surface methodology in which SPF values before and after irradiation has been considered. Consequently, an SPF30 and SPF50 emulsions containing only 9 and 12% total filter respectively and 5% LiS each had been developed. This high boosting effect led to discussions on how LiS interacts, suggesting the involvement of J aggregation, the formation of LiS micelles that would partly encapsulate the o-soluble filters, and the mode of adsorption at the solid-liquid interface of the poly(methyl-methacrylate) plate or the skin.