No abstract

Nobody exactly knows when human beings begun protecting their skin from the sun. Our darkskinned ancestors in Africa had the benefit of natural melanin to avoid sunburn. With migration to cooler regions, humans clothed themselves to avoid frost, losing their protective pigmentation. For cultural reasons, occidentals continued to cover their body up to the XIX th century. After World War I fashion wanted tanned bodies. Oils without protection to UV radiation were used. In 1935 Eugène Schueller, founder of L'Oreal, formulated the first radiation filtering product, "Ambre Solaire Huile". Benjamin Green produced for the soldiers battling in the Pacific a red jelly substance as a physical blocker. The hazards of sun overexposure were already apparent. The product boomed under the brand Coppertone. In 1946 Franz Greiter developed the "Gletscher Créme". In 1956 R. Schulz introduced the concept of the sun protection factor (SPF). All those products protected only against UVB radiation, whose main visible result is erythema. There was still no concern on the more penetrating UVA radiation, and skin cancer prevention nor on several other contemporary issues. Today we benefit from very high SPF products with broad UV protection. Solubility limitations and sensorial properties make them difficult to formulate and stabilize.

There is still an international need to develop broad-spectrum sunscreen products with an adequate UVB/UVA balance, while the approved filters available in the UVA are scarce. Currently, one of the few UVA filters approved in the United States and Europe is tert-butylmethoxydibenzoylmethane (BMDM, avobenzone). However, this compound is unstable from aphotochemical point of view and cannot be used in combination with certain sunscreens. In this paper, we investigate the photochemical behavior of a set of dibenzoylmethanes and chalcones. In particular, we carry out their absorption and emission spectra, evaluate their photochemical degradation, and study their generation of free radicals and singlet oxygen photoproduction. Two compounds resultedin having the basic properties of UVA filters (2 -hydroxy-4-methoxychalcone and 2 -hydroxy-4-methoxydibenzoylmethane). Further studies are proposed, such as formulating the compounds into emulsions or other common cosmetic presentations, as well as combining them with broadly-used UVB filters. We have also considered the need to establish its toxicological profile.