# Recent Trends on UV filters
## 1 Introduction  
The noxious impact of solar radiation was known to many ancient civilizations, and individuals consequently tried to avoid photo-induced damage. Egyptians used natural extracts such as almond oil, calcite powder and clay, rice, and jasmine due to their photoprotective and healing properties [1; 2; 3]. Greeks protected themselves with oils and sands containing minerals during exercise, and these were later used in India for medicinal purposes [1; 4; 5]. Experimental studies about the damaging effects of UV radiation (UVR) in skin started in the early 1800's [3]. Twenty years later, [PERSON] researched the ability of a group of substances to absorb UVR. Acidified quinine sulfate (AQS) was the first compound that was proven to reduce sunburns induced by UVR [5]. After that, [PERSON], in 1891, combined AQS in lotions and created the first sunscreen [4]. The development of UV filters progressed, and, in 1894, [PERSON] and [PERSON] confirmed that some skin disorders, such as erythema and skin cancer, were associated with excessive sunlight exposure without protection [5]. With this evidence, [PERSON] and [PERSON] startedtheir research in this field, culminating in 1928 with the creation of the first formulation offering UVB protection, an emulsion containing benzyl cinnamate and benzyl salicate [2; 6]. Despite all these advances, the first commercially available sunscreen was only marketed in 1935, a creation of [PERSON], the founder of L'Oreal. This sunscreen was called \"Ambre Solaire\" and contained benzyl salicylate [3; 7], the same UVB filter present in [PERSON] and [PERSON]'s formulation [2; 6]. In the 1940's, \(p\)-aminobenzoic acid (PABA) and its derivatives were studied, with PABA derivatives revealed to be more efficient, namely the mono and dialkyl PABA ester derivatives [8]. Over the years, other methodologies were developed to prove the effectiveness and safety of UV filters. PABA was confirmed to be photounstable and a promotor of allergic reactions [9]. Further research confirmed its low photostability, as well as toxic effects, culminating in its ban in the European Union in 2008 [10]. In 1969, the dangerous effects of UVA radiation for the skin became more apparent [11]. The first UVA filters available were benzophenone derivatives. In 1980, only 1% of European sunscreens contained this substance, though this had increased to 35% ten years later [12]. It is important to mention that after the creation of the first sunscreen formulation, \"Ambre Solaire\", this research topic stimulated the scientific community and increased the desire to understand the mechanisms behind sunscreen activity. Sunscreens are products used worldwide but with different definitions and classifications across countries. The United States of America (USA), New Zealand, Canada, and Australia apply the drug regulations to sunscreens [13]. In contrast, in China, Japan, South Africa, and in some countries in South America, sunscreens are regulated as cosmetic products, similarly to the European Union (EU) [13]. UV filters are defined in Cosmetic Regulation (EC) n\({}^{\circ}\) 1223/2009 as \"substances which are exclusively or mainly intended to protect the skin against certain UV radiation by absorbing, reflecting, or scattering UV radiation\" [14]. Annex VI of this regulation mentions the list of approved UV filters for cosmetic use, with a total of 28 compounds being listed, including two inorganics (zinc oxide (ZnO) and titanium oxide (TiO\({}_{2}\))), which can be present in non-nano or nano forms, and 26 organic UV filters. Of all the 26 organic UV filters, biscortizole and trisphenyl tri-azine can also be present in nano forms. One of the controlled parameters is the maximum concentration allowed in the formulation. Over the years, some alterations to the list of European approved UV filters were noted, including both approvals and withdrawals.