Processing red flags
Sodium ferrocyanide
Definition
What it is
Yellow prussiate of soda (sodium ferrocyanide, E535): anti-caking agent used in table salt; a cyanide complex compound that releases hydrogen cyanide under some conditions; banned in some countries.
On the label
Label names covered by this flag
- sodium ferrocyanide
- yellow prussiate of soda
- potassium ferrocyanide
- e535
- e536
Regulation
Regulatory status
No bans or restrictions are recorded for this ingredient in the jurisdictions clearlabel tracks (US, EU, UK, Canada, Japan, Australia/NZ, Brazil).
Explainer
In plain language
Sodium ferrocyanide, sometimes called yellow prussiate of soda, is an anti-caking agent used mostly in table salt and some salt substitutes to keep the crystals from clumping. The closely related potassium ferrocyanide does the same job. Despite the name, the cyanide in these compounds is locked tightly into a stable iron complex, which behaves very differently from free cyanide.
Assessment
Why it is flagged
The word cyanide understandably draws attention, and this flag exists partly to make the ingredient visible. In its 2016 re-evaluation EFSA reviewed sodium and potassium ferrocyanide and set an acceptable daily intake, concluding they were of no safety concern at the levels used in food, while noting some data gaps. The compound is chemically stable, but under strong acid or high heat a cyanide complex can in principle release hydrogen cyanide, which is why regulations control where and how much can be used. The FDA permits ferrocyanides as anti-caking agents within limits, and in the EU they appear as E535 and E536. Clear Label marks it medium severity for transparency and because usage rules differ between countries, not because harm at normal salt intake is established.
In the aisle
Where it commonly shows up
- Table salt and iodized salt
- Salt substitutes and low-sodium salts
- Some seasoning and spice blends
- Bulk and industrial food salt
- Some processed foods where salt is added in bulk
Practical
Reading the label
On labels it appears as sodium ferrocyanide, potassium ferrocyanide, or yellow prussiate of soda, and in the EU as E535 or E536. It is most often found in ordinary table salt, so checking the ingredient line on a salt canister is the easiest place to spot it.
Alternatives
If you want to avoid it
Some people choose salts that use a different anti-caking agent or none at all, such as certain sea salts or coarse salts that flow without additives. Comparing two salt labels usually shows which one includes a ferrocyanide.
FAQ
Common questions
Is the cyanide in sodium ferrocyanide dangerous?
The cyanide is bound tightly inside a stable iron complex and behaves very differently from free cyanide. EFSA reviewed it in 2016 and found no safety concern at the levels used in food, while setting an acceptable daily intake.
Why is it used in salt?
It coats the salt crystals so they stay loose and pourable instead of clumping in humid conditions. Only a very small amount is needed for that effect.
Is sodium ferrocyanide banned anywhere?
Rules on ferrocyanide anti-caking agents vary by country, and some jurisdictions restrict or limit them more tightly than others. In the US the FDA permits them within limits, and the EU allows them as E535 and E536 within set levels.
Citations
Sources
Citation
Primary reference
About this page: the definition, label names, severity, and regulatory chips come from the clearlabel ingredient taxonomy, the same data the scanner uses to score products. Research summaries describe associations reported in published studies, not diagnoses; individual responses vary. Scan any product with clearlabel to see which of its ingredients carry flags.