Aluminum Sulfate

Aluminum sulfate is an astringent/acidic inorganic salt used as a coagulant or styptic; in topical exposure it can lower local pH and denature proteins, making stinging and irritant contact dermatitis more likely, especially on compromised or eczematous skin. Patch testing and clinical experience show it can be irritating (and occasionally problematic when skin barrier is impaired), and its risk increases in leave-on products or higher-concentration/low-pH settings. Given the significant irritation potential in sensitive populations and the likelihood of stinging on broken skin, it warrants a significant irritancy score. Safety Notes: In consumer skincare, aluminum sulfate is most often encountered at very low levels as an astringent/pH-adjuster in toners, aftershaves, and some rinse-off cleansers (commonly around 0.05–1%). The upper end reflects consumer-available high-astringency products such as styptic pencils and alum/“astringent stone” style preparations or very concentrated astringent liquids, where aluminum sulfate can be present in the ~10–20% range (higher levels are generally impractical due to irritation and solubility/stability constraints in typical leave-on skincare).