Properties of Aspalathus linearis extracts as sunscreen ingredients. A biological filtering system for skin photoprotection

The new horizons in the development of sunscreens are based on the discovery of novel active ingredients from natural sources. The objective of the work was to analyze the potential of a combination of Aspalathus linearis (AL) extracts in the enhancement of different biological protection factors of topical sunscreen formulations, as well as their influence in the photostability of standard organic UV filters under simulated solar UV radiation. Various sunscreen formulations were prepared incorporating different concentrations of both non-fermented and fermented AL extracts The UV transmittance properties as well different protection factors (solar protection factor, UVA protection factor, immune protection factor) were analyzed by in vitro techniques (ISO24443:2022) when formulated alone or in combination with the UVB and UVA standard UV filters Octyl-methoxy-cinnamate (OMC) and Butyl-Methoxy-dibenzoyl-methane (BMDBM). Additionally, the protective potential of the natural extracts against photodegradation was evaluated by applying increasing erythemal doses emitted by a solar UV simulator. Water containing AL extracts showed a significant UV absorbance with an absorption peak around 285 nm. In sunscreen galenic formulas, when combinationed with OMC and BMDBM increased up to 50% the protection factors of the sunscreen compared to standard filters alone. AL extracts were also able to protect against photodegradation of BMDBM and OMC under increasing radiation doses up to 14.4 standard erythemal doses. In conclusion, the topical application of both fermented and unfermented AL extracts could appear as excellent sunscreen agents, offering a double benefit increasing the protection values against different biological effects as well as protecting again photodegradation.