Sodium Bisulfite

Sodium bisulfite is a reducing agent/antioxidant preservative used at low levels (often ~0.1–1%) but is a well-documented irritant and can provoke adverse reactions in sensitive individuals, especially those with eczema or sulfite sensitivity. It can cause stinging, erythema, and eczematous reactions on compromised skin, and its sensitization/trigger potential warrants careful introduction and patch testing rather than assuming it is “gentle.” Safety Notes: In commercial cosmetics, sodium bisulfite is most often used at very low levels (around 0.001–0.05%) as an antioxidant/reducing agent to protect oxidation-prone ingredients (e.g., certain dyes, botanical extracts, or to stabilize some solutions), with the lowest levels commonly seen in leave-on serums/creams where odor/irritation and sulfite sensitivity are concerns. Higher levels are mainly observed in rinse-off products—especially hair color/bleach-related and some cleansing systems—where it can function as an oxygen scavenger/reductant, with consumer-available products reaching about 0.5–1.0%. While not universally capped by a single global maximum in the same way as some preservatives, practical sensory/compatibility limits and sulfite-allergy labeling considerations typically constrain leave-on use to the low end of this range.