Magnesium Sulfate

Magnesium sulfate (Epsom salt) is primarily a humectant/osmotic salt used in rinse-off soaks or low levels in leave-on formulas; as a high-ionic-strength ingredient it can sting and increase dryness, especially on compromised or eczematous skin. Clinical experience and patch/irritation testing generally show low sensitization risk, but irritation is possible at higher concentrations or on barrier-damaged skin, so it warrants a mild score for patient safety. Safety Notes: In consumer skincare, magnesium sulfate (Epsom salt) appears at very low levels (~0.01–0.5%) as an incidental/minor ionic adjuster or to support viscosity/texture in emulsions and masks, while still being listed on-pack. The highest observed OTC concentrations are in salt-based body scrubs, bath/shower exfoliating pastes, and rinse-off mud/salt masks where magnesium sulfate can function as the primary particulate/solids phase, commonly reaching ~10–25% in real-world products (higher is more typical for bath soaks, which are not always categorized as skincare leave-ons). Leave-on facial products are generally constrained to much lower levels due to tackiness, potential irritation/osmotic effects, and solubility/water-activity impacts, whereas rinse-off formats tolerate substantially higher loadings.