Sodium Sulfite

Sodium sulfite is primarily used as an antioxidant/preservative in low concentrations, but sulfites are well-documented to cause irritation and allergic-type reactions in a subset of sensitive individuals, with positive patch-test reactions reported (especially in eczematous skin). While many users tolerate it, the risk is meaningfully higher than baseline for compromised barriers and reactive populations, so I score it as a moderate irritant where patch testing is prudent. Safety Notes: In consumer skincare, sodium sulfite is most often used as an antioxidant/reducing agent (oxygen scavenger) to protect oxidation-sensitive actives and fragrances; at the low end it appears around ~0.05–0.2% in leave-on serums/creams and some rinse-off cleansers mainly for stabilization. Higher-strength OTC products (especially rinse-off cleansing systems, exfoliating/brightening products, and some self-tan/anti-oxidation specialty formulas) can use it around ~0.5–2.0% to provide stronger reducing/antioxidant and anti-browning effects, with >2% being uncommon in mainstream consumer skincare due to odor/irritation and sulfite-sensitivity considerations.