Sodium Bisulfite

Benefits
Antiseptic

What is Sodium Bisulfite?

Sodium bisulfite is a synthetic inorganic salt with the chemical formula NaHSO3, derived from sulfurous acid. It belongs to the category of preservatives, antioxidants, and hair conditioning agents in cosmetics. This compound works by releasing sulfur dioxide to inhibit microbial growth and prevent spoilage, ensuring product safety during use. As an antioxidant, it neutralizes free radicals that could degrade oils, colors, or active components, maintaining formula integrity over time. In hair care, it functions as a reducing agent in waving or straightening treatments, disrupting disulfide linkages in keratin proteins to enable structural changes that hold after processing. It also provides antiseptic action against certain pathogens. Typically found in rinse-off hair products, shampoos, and conditioners at controlled levels for efficacy without excess residue.

Comedogenic Rating 0/5 Low risk of clogging pores
EWG Safety Rating 2-3 View on EWG →
PubChem View on PubChem →

Roles in Formulation

This ingredient serves the following purposes in cosmetic formulations:

Antioxidant
Slows oxidation of oils, fragrances, and sensitive actives to improve shelf life and reduce rancidity or color change; sometimes also supports skin protection from oxidative stress.
Hair waving or straightening
Reshapes hair by breaking and reforming bonds in the fiber (often via reducing/oxidizing steps), enabling permanent waves or straightening services/products.
Reducing agent
Causes reduction reactions, often used in hair perming.
Preservative
Protects the product from microbial contamination during storage and use, helping maintain safety, stability, and shelf life.

Benefits

Supports product preservation by controlling microbial growth.

Extends shelf life by preventing oxidation of sensitive ingredients.

Facilitates hair reshaping in perming or straightening formulas.

Who It's For

A quick guide for who this ingredient may suit (and who should be cautious).

Who May Benefit Who Should Avoid
Individuals using permanent hair waving or straightening products.
Those with known sulfite sensitivities.
Users of formulations with oxidizable oils or fragrances.
Asthmatics prone to sulfite reactions.
People seeking stable, long-lasting cosmetic products.
Individuals with highly reactive skin conditions.

Safety Notes

  • Rated low to moderate hazard by safety assessments for typical cosmetic use.
  • May cause irritation or allergy in sulfite-sensitive individuals.

Frequently Asked Questions about Sodium Bisulfite

What does sodium bisulfite do in cosmetics?

It acts as an antioxidant to prevent oxidation, preservative against microbes, and reducing agent for hair reshaping.

Is sodium bisulfite safe for skin?

Generally considered safe in cosmetics per expert reviews, though sulfite-sensitive people may react.

In which products is it common?

Found in hair perms, shampoos, conditioners, and stabilizing formulations.