Saccharomyces/Potassium Ferment

Saccharomyces/potassium ferment is a yeast-derived ferment filtrate used as a conditioning/humectant component, typically at low percentages, but ferments contain complex mixtures (proteins/peptides, organic acids, residual cell components) that can trigger stinging or dermatitis in reactive or eczema-prone skin. Clinical experience and patch-test literature on yeast/ferment derivatives show they are usually tolerated yet not reliably "inert," with occasional irritation or sensitization reported. Given the unpredictability of ferment byproducts and heightened risk in compromised barriers, I rate it as mild rather than gentle for patient safety. Safety Notes: In commercial skincare, Saccharomyces/Potassium Ferment is most often used as a bio-ferment/conditioning active at low levels (~0.1–1%) in leave-on toners, essences, serums, and moisturizers, where it functions as part of a broader fermented-complex. Higher-strength consumer-available products (primarily leave-on ampoules/essences marketed around “ferments” or “probiotic/biome” benefits) can reach ~5–10% when the ingredient is supplied as a standardized ferment filtrate and the formula is built around it; above this, odor, color, and stability/preservative loading typically become limiting in OTC formats. Rinse-off cleansers commonly sit toward the low end due to short contact time and cost/compatibility considerations.