What it is
In the register’s words: “Sodium Bisulfite is the inorganic salt.”
- EU register name (INCI)
- SODIUM BISULFITE
- CAS number
- 7631-90-5
- EC number
- 231-548-0
What the register lists it for
These are the uses the European Commission’s CosIng register lists for Sodium Bisulfite in any cosmetic, hair roles first. They say why a maker might add it, not what it does in one formula, and they aren’t a safety rating.
- Hair waving or straightening
-
The register’s role for ingredients that can change the hair’s structure in a perm or relaxer. None of the products here is a perm or relaxer; an ingredient with this role is usually on their labels for another listed use.
Register definition: “Modifying the chemical structure of the hair, allowing it to be set in the style required (permanent waves or hair straightening).”
- Antioxidant
-
Slows the oxygen damage that makes oils go rancid in the bottle. Vitamin E (tocopherol) is the common one.
Register definition: “Inhibiting reactions promoted by oxygen, thus avoiding oxidation and rancidity.”
- Preservative
-
Stops bacteria, mold and yeast growing in the bottle. EU law allows only the preservatives on its own list for this role.
Register definition: “Exclusively or mainly intended to inhibit the development of micro-organisms in the cosmetic product. All authorised preservatives are substances in the positive list of Annex V to the Cosmetics Regulation 1223/2009.”
- Reducing
-
Changes another ingredient chemically by adding hydrogen; in hair products, mostly in perms and colors.
Register definition: “Changing the chemical nature of another ingredient by adding hydrogen (or removing oxygen).”
Where it sits on each label
US labels list ingredients from most to least, except that those at 1% or less may follow in any order. A name near the top is a large part of the formula. A label doesn’t mark where the 1% point falls, so further down, the order says little about how much is in it.
- Clarifying shampoos 1 label First five names: 0 of 1 Clarifying shampoos without it
Every label, product by product (1)
- Ouidad Water Works Clarifying Shampoo Clarifying shampoo 18th of 33 names
Each line runs from the first name on a label to the last; a dot is where this ingredient sits. Makers change formulas now and then; if the list on your bottle differs, go by your bottle.
Your next step
Other hair waving or straightening ingredients on these labels
- Sodium Sulfite 5 labels
Updated · The name, numbers and uses come from the European Commission’s CosIng entry (CC BY 4.0); we write the uses in US spelling and put the hair ones first. The labels are each maker’s own. The order rule is the FDA’s Cosmetics Labeling Guide. All our sources are on the Sources page.