A critical review on layered double hydroxides: Their synthesis and application in sunscreen formulations

Abstract Overexposure to solar ultraviolet (UV) radiation is indisputably a major risk factor to the genesis and development of skin cancer, especially non-malignant melanoma. In order to counter the adverse effects of UV radiation the use of sunscreens remains the most sought-after form of protection. The active ingredients in these products are the UV-filters which can be organic or inorganic substances. However, with increasing evidence of systemic uptake, photodegradation and possible carcinogenicity of particularly organic UV filters, the use of nanoparticles as the delivery vehicles for these molecules presents potential advantages. These include retention of the sunscreen on the surface of the skin, prevention of possible dermal penetration, and UV attenuation by both absorption and scattering. Layered double hydroxides (LDH) are one of the cheapest and ever-evolving inorganic materials that can be made use of in this respect. In this review, the current methods of synthesis for LDH used in sunscreen preparations as well as the post-synthesis modifications, are reviewed. New approaches for the incorporation of neutral sunscreen actives in LDH are also addressed. Finally, examples of sunscreen filters that have been intercalated into LDH are provided together with an assessment of their efficacy.