What Is Ammonium Bisulfite?
Ammonium bisulfite, also called ammonium hydrogensulfite, is a salt formed from ammonia and sulfurous acid. It appears as a clear to yellowish liquid when dissolved in water and gives off a mild sulfur smell. The compound has been known since the 19th century when chemists explored sulfur-based preservatives for foods and textiles. Its move into cosmetics happened in the mid-20th century after researchers discovered that its gentle reducing power could soften the bonds inside hair without the harshness of stronger chemicals.
Commercially, manufacturers create ammonium bisulfite by bubbling sulfur dioxide gas through an aqueous ammonia solution under controlled temperature and pH. The result is a stable, water-soluble ingredient that blends easily with other cosmetic raw materials.
You will most often find ammonium bisulfite in home or salon hair-texture kits such as permanent waves and chemical straighteners. Its mild preservative action also makes it useful in some liquid skin treatments, masks and lotions where formulators want to limit microbial growth without relying on parabens.
Ammonium Bisulfite’s Cosmetic Benefits/Uses
Below are the main ways this ingredient supports cosmetic formulas
- Hair waving or straightening: Ammonium bisulfite breaks some of the disulfide bonds inside hair strands, allowing stylists to reshape curls into waves or smooth out natural texture. Because it is milder than thioglycolic acid it can deliver results with less odor and reduced risk of over-processing
- Preservative: Its acidic, sulfur-based nature creates an environment that discourages bacteria and molds from growing, helping water-rich products stay fresh on the shelf
- Reducing agent: In formulas that contain oxidizing dyes or other reactive ingredients, ammonium bisulfite can act as a gentle antioxidant, stabilizing color and preventing unwanted changes during storage
Who Can Use Ammonium Bisulfite
Most skin and scalp types tolerate ammonium bisulfite well because it is water soluble and rinses away cleanly. Normal, oily and combination skin generally see few issues while very sensitive or eczema-prone skin may feel stinging or develop redness if the product is left on too long or applied to broken areas.
The compound is synthetically produced from simple mineral sources so it is suitable for vegans and vegetarians. As always anyone concerned about animal testing should verify the brand’s cruelty-free status.
Current safety data show no specific risks for pregnant or breastfeeding women when ammonium bisulfite is used in rinse-off hair products. That said this is not medical advice and those who are pregnant or nursing should run any cosmetic routine past their healthcare provider to be safe.
The ingredient does not absorb ultraviolet light and is not known to cause photosensitivity. It is also non-comedogenic so it will not clog pores if a small amount comes into contact with facial skin during a hair treatment.
Potential Side Effects/Adverse Reactions
Reactions to topical ammonium bisulfite vary from person to person. The points below list potential side effects that can occur even though most users experience none when the product is formulated and used correctly.
- Skin and scalp irritation It can cause redness stinging or itching especially on sensitive or broken skin
- Allergic contact dermatitis Though uncommon some people may develop delayed swelling or rash after repeated exposure
- Excess dryness or brittleness in hair Overprocessing can strip moisture leaving strands rough and prone to breakage
- Temporary sulfur odor The characteristic smell may linger on hair or skin and can bother individuals with fragrance sensitivities
- Eye or airway discomfort Fumes released during heat styling may make eyes water or trigger mild coughing
If any of these effects occur discontinue use immediately and consult a medical professional.
Comedogenic Rating
Rating: 0/5 Ammonium bisulfite is a small, water-soluble salt that rinses away fully and does not leave an oily film behind. Because clogged pores are usually triggered by heavy waxes or oils, this lightweight ingredient poses virtually no risk of causing blackheads or pimples. It is therefore suitable for people who break out easily. Since it is used mainly in rinse-off hair products, any brief contact with facial skin is unlikely to create issues.
Summary
Ammonium bisulfite serves three key roles in cosmetics: it reshapes hair by gently breaking some internal bonds, it guards formulas against spoilage through light antimicrobial action, and it works as a mild reducing agent to keep colors and other actives stable. You will mostly see it in perm or straightening kits rather than everyday skin care, so its popularity sits in a niche spot within the larger beauty market.
Current research and long-standing salon use show that it is safe for most people when applied as directed, with irritation being the main concern if overused. As with any new cosmetic product it is smart to run a small patch test first just to be sure your skin and scalp stay comfortable.