# Unveiling the Role of Minerals and Trace Elements of Thermal Waters in Skin Health
## 2 Minerals, Trace Elements, and Other Compounds of TSW in Skin Health
### Trace Elements
#### 2.3.1 Selenium  
The most-studied TSW containing selenium is La Roche-Posay TSW. In addition to calcium, La Roche-Posay TSW is rich in selenium and strontium, to which researchers attribute the antioxidant properties of this thermal water [84]. Studies comparing La Roche-Posay TSW with distilled water and water with the same selenium concentration as La Roche-Posay TSW showed that the La Roche-Posay TSW had a greater protective effect against oxidative stress induced by UVB light than controls in human skin fibroblasts [45].  
To investigate the effects of La Roche-Posay TSW, several studies have been performed over the last twenty years. In vitro studies were performed in which human skin fibroblasts were cultured and exposed to oxidative stress from UVA radiation in the presence or absence of La Roche-Posay TSW, showing that selenium-glutathione peroxidase and superoxide dismutase activity was higher in fibroblasts cultured in medium containing La Roche-Posay TSW than in other media [46]. A study carried out on human keratinocytes after exposure to increasing UVB doses, showing better resistance with better cell survival and a reduction in IL-1\(\alpha\) cytokine release in cells cultured in medium containing La Roche-Posay TSW in comparison with cells cultured in medium containing demineralized water [47]. An in vitro study evaluated the modulatory effects of media containing selenium or strontium salts as well as La Roche-Posay TSW. These effects were evaluated using a reconstructed model of biopsies of healthy skin or skin with atopic dermatitis for the production of IL-1\(\alpha\), IL-6, and TNF-\(\alpha\). In the three media, after 10 days of culture, the production of these three cytokines was lower in the inflamed skin than in the healthy skin. With strontium salts, the skin's selective inhibitory effect on IL-1\(\alpha\) production was less evident, but the inhibitory effect for TNF-\(\alpha\) was greater. At intracellular and extracellular levels, selenium and strontium salts showed a modulating effect in decreasing IL-6 production [48].  
Furthermore, it has been suggested that selenium-rich thermal water could play an important role in the prevention of UV damage, as studies have shown that La Roche-Posay TSW is able to reduce IL-1\(\alpha\) release in irradiated keratinocytes, increase selenium-dependent glutathione peroxidase activity, and decrease the production of lipoperoxides in irradiated fibroblast [49].  
Additionally, [PERSON] et al. [24], comparing different waters, showed that La Roche-Posay TSW was able to reduce IL-6 levels and the formation of ROS after UVB irradiation. The authors suggested that the observed effects could be related to the high selenium content (53 \(\upmu\)g/L), which is a co-factor for glutathione peroxidase, a key enzyme in the elimination of ROS.  
As has been previously mentioned, La Roche-Posay selenium-rich spring water was also used in the treatment of scars after pediatric plastic surgery and has been shown to be able to reduce pruritus, soften the inflammatory appearance, and facilitate the elimination of crusts and prevent the formation of new ones [84].  
Additionally, La Roche-Posay selenium-rich spring water was found to reduce PASI scores by 47 \(\pm\) 4% (\(p\) < 0.05), and interestingly, 8% of patients were completely cleared and 48% improved by more than 50%. Changes in the microbiome profile were also found [50].