# Chaves Thermal Spring Water Impact on Skin Health: Potential Cosmetic Application
## 4 Discussion
It is also known that mineral salts such as selenium, copper, manganese, and zinc have an important role as antioxidants, with selenium being used in the effective removal of peroxides from cytosol and cell membranes, while the cytosolic superoxide dismutase requires copper to activate its antioxidant properties [50]. For example, Avene, Uriage, and Vichy thermal spring waters, as well as dead sea water, present high contents of some of these minerals, and in vitro experiments have demonstrated their antioxidant capacity by reducing the generation of ROS in UV-exposed skin or cells [26; 51; 52]. In contrast, Chaves thermal spring water did not show antioxidant activity in comparison to vitamin C via the ABTS and DPPH methods. This result might be explained by its mineral composition, in which sodium is dominant. Previous studies have reported that thermal spring waters have a positive effect on extracellular matrix (ECM) proteins, including collagen and fibronectin, as its major components. Collagen is responsible for skin elasticity and flexibility, while fibronectin plays an important role in the ECM organization and stability [26; 51; 52]. For instance, in vitro studies have demonstrated that Blue Lagoon and Nitrodi's spring waters significantly increased the levels of collagen 1a1 and 1a2 in human epidermal keratinocytes and fibroblasts [53; 54]. It has been also reported that the silicon content of thermal spring water might be related to collagen synthesis via the activation of hydroxylation enzymes that are crucial for forming the collagen network, thereby improving skin elasticity and strength [55]. Although Chavesthermal spring water contains 37.20 mg/L of silicon, this concentration was not sufficient to increase the collagen synthesis in nHDF cells. Moreover, in vitro studies have demonstrated a promotion in the fibronectin deposition with Nitrodi's spring water [53]. In contrast, our results demonstrated no significant increase in the production of fibronectin after the incubation of nHDF cells with Chaves thermal spring water. The human skin acts as the exterior interface of the human body with the environment, meaning that the exposure to air pollution or UV radiation might have a negative impact on skin health, leading to inflammatory processes and ROS production. Several changes have been reported to occur in skin cells after their exposure to pollution factors, such as in lipid composition and protein oxidation, and increases in inflammation markers and oxidative stress [16]. In the present study, Chaves thermal spring water significantly decreased the levels of IL-6 in HaCaT cells exposed to urban air pollution particles. This result indicates the soothing potential of Chaves thermal spring water, which is in accordance with the published data for other thermal spring waters [56]. In addition to in vitro experiments, we measured the skin biometric parameters on the forearms of volunteers, demonstrating that Chaves thermal spring water significantly decreased the TEWL without changing the hydration level (comparing day 0 and day 16). The values of the TEWL and hydration level are associated with the health of the skin as well as the age of individuals, and sometimes they are inversely related [57]. Thus, both skin parameters are frequently used in dermatology and cosmetology to evaluate the integrity of the skin barrier and to assess the efficacy of topical products, such as thermal spring waters [40; 57]. Our results suggested that Chaves thermal water might be used to restore the skin barrier function due to the decrease in the TEWL, making it helpful for individuals with skin diseases, who are associated with higher values of TEWL in comparison to the unaffected [58; 59]. [PERSON] et al. [58] reported that the TEWL was significantly higher in psoriatic plaques and atopic dermatitis cemetuous lesions than in uninvolved or healthy skin.