The benefits of sulphur on the skin.

In vitro, it has been demonstrated that sulphur may have a slight antibacterial activity. It is believed to have an inhibitory effect on the growth of Propionibacterium acnes, certain streptococci, a moderate effect against most staphylococcal bacteria (Staphylococcus aureus, Staphylococcus epidermidis) and no activity against Gram-negative bacteria. This antibacterial action is thought to result from the inactivation of the sulfhydryl groups contained in bacterial enzymatic systems. Thus, sulphur could potentially aid in combating acne bacteria, reducing inflammation and preventing future acne outbreaks. However, the exact mechanism of action of sulphur in the asymptomatic treatment of acne is not fully understood.

Sulphur, more specifically hydrogen sulphide, is believed to have physiological functions as an endogenous cellular signalling molecule in the regulation of inflammation via NF-κβ. It is thought to downregulate the production of pro-inflammatory cytokines (IL-8, IL-1β, TNF-α, IL-6 and IL-10).

This reflects a reduction in oxidative stress, which can contribute to reducing the inflammatory state.

Sulphur is believed to have an exfoliating effect on the upper layers of the epidermis, meaning it would remove dead cells from the skin's surface that cause pore blockage. This could consequently reduce the formation of both open and closed comedones. However, the precise mechanism of this effect is unknown but, according to some studies, it likely depends on the interaction of sulphur with cysteine, an amino acid present in keratinocytes, leading to the production of hydrogen sulphide (H2S) and cystine.

Sulphur + 2 cysteine ==> cystine + hydrogen sulphide

Indeed, hydrogen sulphide is believed to have a keratolytic activity by breaking down keratin, particularly when sulphur is applied at higher concentrations. Similarly, the smaller the size of the sulphur particles, the greater this interaction and the higher the efficacy. As for the formed cystine, it is a constituent of the horny layer and this reaction would promote the normal keratinisation of skin cells. Consequently, sulphur-based products could potentially be an effective alternative to products containing salicylic acid or benzoyl peroxide, especially if you have sensitive skin and cannot tolerate these ingredients.

Sulphur is believed to purify the skin by absorbing excess sebum. This removal of sebum from the sebaceous glands could help to minimise pore congestion, thereby preventing and reducing skin breakouts (spots, blackheads, etc.).

Seborrheic dermatitis, dandruff, and pityriasis versicolor are common chronic skin infections caused by yeasts of the Malassezia genus. However, sulphur is believed to have a potential antifungal effect, an effect that has been primarily studied by botanists interested in plant fungal infections. Researchers have revealed that pentathionic acid (H2SsO6), which is toxic to fungi, is formed by bacteria of the skin microbiota, as well as by keratinocytes from locally applied sulphur.

Hydrogen sulphide also appears to play a role. However, studies in vitro suggest that sulphur has little or no antifungal activities, but rather they would result from its keratolytic effects by promoting the removal of fungal spores from the stratum corneum. Sulphur is often used in conjunction with salicylic acid for the treatment of these conditions, as they have a synergistic keratolytic action.

Although data is scarce, sulphur is believed to have a parasiticidal effect on Sarcoptes scabiei, the mite responsible for scabies, and also on Demodex folliculorum, a skin parasite considered one of the main causes of rosacea. This toxicity of sulphur has been attributed to the formation of hydrogen sulphide and pentathionic acid. As in fungal infections, the keratolytic effect of sulphur may also help to dislodge parasites from the corneal layer.

Hydrogen sulphide could have an antioxidant application through its conversion into hydrogen sulphide. It would counteract oxidative stress by acting as a scavenger of reactive oxygen species (ROS) and reactive nitrogen species (RNS), and would enhance the levels of superoxide dismutase (SOD) and glutathione, thereby strengthening the antioxidant status and providing protection against oxidative damage to DNA and proteins.

Its antioxidant effects exist, in part, because it contributes to the synthesis of methionine, an amino acid that combats cellular ageing. As for cysteine, this amino acid participates in the synthesis of proteins necessary for the skin, such as collagen and melanin.

• Document fournisseur.

• CARTER D. & al. Sulfur revisited. Journal of the American Academy of Dermatology (1988).

• NICOL K. & al. The use of sulfur in dermatology. Journal of Drugs in Dermatology (2004).

• ORTEGA-RINCÓN & al. Balneotherapy, immune system, and stress response: A hormetic strategy? International Journal of Molecular Sciences (2018).

• NATAF S. & al. Molecular mapping of hydrogen sulfide targets in normal human keratinocytes. International Journal of Molecular Sciences (2020).