Sulphur to alleviate skin affected by psoriasis?

Considering the potential for side effects from long-term exposure to various systemic treatments for psoriasis, sulphur balneotherapy could represent a useful alternative for the treatment of mild to moderate psoriatic lesions. Indeed, sulphur-based remedies have been used for centuries to treat various dermatological conditions such as psoriasis.

A small clinical trial revealed that all 10 patients suffering from psoriatic plaques showed a significant improvement in the elasticity of skin components (elastic fibres, etc.) and a restoration of its hydration level, after a bath at a temperature of approximately 34˚C - 35˚C in thermal water containing a high level of sulphur (173 mg/L) for a duration of 20 minutes over 12 days, compared to the skin of controls showing no obvious skin lesions. They thus reported a reduction in psoriasis symptoms, namely a decrease in the thinning of psoriatic plaques and a reduction in the intensity of redness.

By what mechanisms?

The action of sulphur on the skin is believed to be due to its interaction with cysteine and its catabolites contained in keratinocytes. The sulphur that penetrates the skin is oxidised into hydrogen sulphide and triggers various physiological responses.

• Anti-inflammatory: Sulphurous water has demonstrated its ability to inhibit the proliferation of T lymphocytes, as well as the production and/or release of pro-inflammatory cytokines (IL-2, IFN-γ), thereby deactivating the main players in the inflammatory response in keratinocytes. It can also inhibit the expression of immune system mediators induced by TNF-α (E-selectin and ICAM-1).

• Anti-proliferative: It has been demonstrated that the exogenous application of hydrogen sulphide (H2S) reduces the proliferation of human keratinocytes by decreasing the expression of the vascular endothelial growth factor (VEGF), through a cascade of intracellular reactions.

In a 2023 study, researchers sought to assess the impact of hydrotherapy on the skin microbiome in 16 patients with plaque psoriasis. The composition of microbial communities was similar on psoriatic plaques and unaffected healthy skin, both before and after balneotherapy. The study reveals that balneotherapy sessions over a 3-week period (sulphur content of 3.2 mg/L; bath temperature at 36°C; neutral pH; five times per week) significantly increased the level of the genus Leptolyngbya (potential antioxidants, anti-inflammatories, anti-proliferatives), and decreased the quantity of the genus Flavobacterium genus (enhancing the growth of Cyanobacteria, such as Leptolyngbya), whether on non-lesioned skin or skin affected by psoriasis.

Limitations to studies?

Although the trend observed confirmed the effects of balneotherapy on psoriasis, these studies notably have limitations. The sample size in the studies is not sufficient for a detailed statistical analysis. Moreover, the characteristics of mineral spring waters differ from one study to another, with different sulphur contents and the presence of other minerals (magnesium, calcium, iron, hydrogen carbonate, etc.). It is therefore not straightforward to determine the effects of sulphur on psoriasis.

However, sulphur-rich water bath therapy appears to have proven itself as a promising therapeutic strategy for clinically improving plaque psoriasis, not to mention that serious adverse effects following this type of therapy are rare. On the other hand, the effects and efficacy of sulphur thermal therapy on psoriasis are only partially understood. Further studies are required.