Uncovering the efficacy of a natural homemade sunscreen in protection from ultraviolet radiation.

In Australia, skin cancer has the highest incidence of all cancer types, where Therapeutic Goods Association-approved, broad-spectrum sunscreens are recommended to prevent skin carcinogenesis. Commercial sunscreen ingredients, however, have been associated with negative impacts on human health, animal health and the environment. Together, the perceived harmful effects of commercial sunscreens have driven a trend towards home formulation of natural sunscreens, recipes for which are widely available online. Scientific evidence to support the efficacy of natural sunscreens, however, is lacking. We tested the efficacy of a natural homemade sunscreen (NHSS) published online by a wellness blogger with the aim to determine its photoprotective properties, beyond its ability to protect against erythema, compared to a commercially available SPF50 + sunscreen. The NHSS contained almond oil, coconut oil, shea butter, beeswax, red raspberry seed oil, carrot seed oil and zinc oxide. Skin explants were treated with either a commercial SPF50 + sunscreen, NHSS or base lotion prior to ultraviolet irradiation. Skin explants were assessed using immunohistochemistry for the levels of UVR-induced DNA damage in the form of cyclobutane pyrimidine dimers and 8-oxo-7, 8-dihydro-2'-deoxyguanosine, as well as for sunburn cells and epidermal thickness. We demonstrate herein that NHSSs can reduce UVR-induced DNA damage and epidermal thickness, but do not effectively protect against the generation of sunburn cells. In comparison, SPF50 + sunscreen provided effective protection against all investigated parameters. These factors, however, are markers of short-term UVR-induced damage and there is as yet no evidence for NHSSs in prevention of skin carcinogenesis. Therefore, we recommend the continued use of TGA-approved commercial sunscreens for sun protection. Further studies are required to test water resistance, variation in homemade formulation, shelf life, and protection against skin carcinogenesis in a chronic UVR model.