# Recent Trends on UV filters
## 3 Results
### Evolution of the Use of UV Filters  
When compared to 2015, the top five UV filters in sunscreens marketed in 2021 remained the same (Figure 6). It is relevant to highlight that avobenzene was the most used organic UV filter in both periods of analysis, with usage frequencies higher than 65%. On the contrary, a change in the usage frequency of bis-ethylhexyloxyphenylenol methoxyphenyl triazine, ethylhexyl salicylate, and octocrylene was observed. The usage frequency of bis-ethylhexyloxyphenyl methoxyphenyl triazine (Tinosorb S\({}^{\circledapprox}\)) (2015: 24.6% and 2021: 45.3%) almost doubled in a timespan of six years, probably due to its high photoprotective effectiveness. This triazine UV filter is a broad-spectrum photoprotective agent, and additionally possesses interesting photostable characteristics that make it a good photoprotective and photostabilizing agent of unstable UV filters, which might explain the increased usage. In contrast to what happened to triazine UV filters, the usage of ethylhexyl salicate (2015: 39.4% and 2021: 36.9%) and octocrylene (2015: 51.7% and 2021: 48.4%) decreased over the analyzed period by around 10%. Ethylhexyl salicate is a good UVB absorber; however, it tends to suffer from photoisomerization and potentially induces some environmental toxicity [26]. On the other side, octocrylene could be transformed into a benzophenone derivative through a retro-aldol condensation reaction, which increases its phototoxic potential and leads to negative environmental effects [27]. Additionally, this toxic benzophenone derivative possesses chemical similarities to a hydroxylated derivative of benzophenone-type compounds that were already reported as possessing endocrine disrupting activity [27; 43], evidencing possible cytotoxic effects and its potential to act as an endocrine disrupter agent.  
Among the available forms of inorganic UV filters, the collected data between 2015 and 2021 showed an increasing tendency towards the use of the inorganic UV filter TiO\({}_{2}\), reaching usage frequencies of 24.1% and 10.4% in 2021 for its nano and non-nano forms, respectively. This is particularly evident for non-nano TiO\({}_{2}\), whose usage more than doubled in six years (from 4.7% to 10.4%). With respect to ZnO, decreased usage was found for the non-nano form, while nano ZnO was similarly used in both periods of analysis. The reasons for the increased use of TiO\({}_{2}\) are not clear but might be explained by its ability to offer broad-spectrum action and higher SPF values, as well as by the toxicity issues that affect other organic filters.  
Methylene bis-benzotriazolyl tetramethylbutylphenol (Tinosorb M\({}^{\circledapprox}\)) is considered a hybrid UV filter due to its physical-chemical behavior and ability to reflect and absorb UV radiation [44]. Additionally, it can also act as a good photostabilizer of other UV filters [44]. However, in the period of analysis, a decrease of almost 50% in the usage frequency of its nano form in sunscreens was observed (2015: 19.5% and 2021: 10.4%). The revised document related to this nano filter, published by the Scientific Committee on Consumer Safety (SCCS), reported that studies about acute oral and dermal toxicity, skin irritation, and skin sensitization for the nano-sized material were not provided [45]. Additionally, some allergic contact cases were reported concerning this UV filter in its non-nano form (11 cases in European countries) [46]. Consequently, it was recommended that TinosorbM\({}^{\text{\textcircled{\text@b}}}\) be included into the European photopatch test baseline series [47], which could have influenced the decrease in use of this filter in sunscreens available on the market in 2021.  
Four organic UV filters, namely disodium phenyl dibenzimidazolele tetrasulfonate (DPDT), phenylene bis-diphenyl triazine (Triasorb\({}^{\text{\textcircled{\text@b}}}\)), nano tris-biphenyl triazine (TBTP), and isoamyl \(p\)-methoxycinnamate (IMC), only appeared in the analysis performed in 2021, with usage frequencies lower than 5%.