# 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
### Other Compounds
#### 2.4.2 Sulfur and Hydrogen Sulfide  
[PERSON] et al. [98] revised the role of H\({}_{2}\)S in dermatological diseases, stating that most of the effects of H\({}_{2}\)S are strongly dose- or concentration-dependent, and the effects of several H\({}_{2}\)S-releasing compounds, such as Na\({}_{2}\)S, NaHS, and GY4137 (H\({}_{2}\)S donor), among others, can be potential therapeutic tools for the treatment of a variety of skin diseases by exerting anti-inflammatory, anti-purriginous, cytoprotective, pro-angiogenic, and immunomodulatory actions. And, later on, [PERSON] et al. [99] summarized the latest research progress on H\({}_{2}\)S-mediated effects, highlighting its antioxidant effect. [PERSON] et al. [100] investigated the role of H\({}_{2}\)S in wound healing, concluding that, overall, H\({}_{2}\)S suppressed skin fibroblast proliferation via oxidative stress alleviation and necroptosis inhibition.  
Sulfur occurs with four main valences, i.e., 2\({}^{-}\), 3\({}^{+}\), 4\({}^{+}\), and 6\({}^{+}\), and depending on the oxidation state, large amounts of oxyacids can be produced, as well as sulfides. In mineral-medicinal waters, compounds with valence 2\({}^{-}\), such as hydrogen sulfide (SH\({}_{2}\)), sulfhydrates (SH\({}^{-}\)), and sulfides (S\({}^{-}\)), and with 6\({}^{+}\) status, such as sulfates are of interest [101]. To exert its beneficial effects, sulfur spring water must contain a reasonable amount of H\({}_{2}\)S or HS\({}^{-}\) and thus have a relatively acidic pH [102]. Studies, both in vitro and in vivo, on primary psoriatic lesions have demonstrated that hydrogen sulfide can not only reduce the basal expression and secretion of IL-8 but also interfere with IL-17- and IL-22-induced IL-8 production [103].  
Sulfur thermal spring waters (also called sulfureous TSW and sulfide TSW) are used in balneo-dermatology to treat dermatological disorders such as psoriasis and AD. They have anti-inflammatory, keratoplasty, antipurritic, antibacterial, and antifungal effects [104]. Other research has reported that sulfureous TSW could induce the release of IL-10, an anti-inflammatory cytokine, as demonstrated in an in vitro study [105], despite the fact that the precise mechanism has not been completely elucidated. In vitro studies have shown the important dose-dependent inhibitory effect of sulfur spring waters on mitogen-induced T lymphocyte proliferation and IL2 production [106]. Additionally, sulfureous TSW boosts the antioxidant capacity and reduces oxidative stress levels in the human body [107]. Other studies have shown that La Bourboule TSW, a sulfurous spring water, could improve wound healing by controlling keratinocyte physiology; the authors suggested that one of the mechanisms of La Bourboule TSW could be the modulation of various inflammation regulators at the mRNA and/or protein levels [57].  
An observational study in patients suffering from psoriasis was carried out to assess the efficacy and safety of balneotherapy with hydrocarbonate- and sulfur-rich water in combination with emollient application in mild-to-moderate plaque psoriasis, as well as to study the influence on the skin physiology of lesional and non-lesional skin. The results showed an improvement in PASI scores, stratum corneum hydration, and itching and skin dryness [58].  
Finally, it is worth mentioning the PSOTERMES study on psoriasis, which included five French thermal baths, including Molito-Les-Bains with sulfurous waters, which showed that thermal spring curing is effective in psoriasis, although the compounds in the thermal waters that may be involved in the observed improvements were not specified. In addition, it should be noted that an improvement was obtained in the VAS pruritus score, one of the most annoying symptoms of psoriasis [59].