E-numbers / Other additives / E535
also: Yellow prussiate of soda · sodium hexacyanoferrate(II)
An anticaking salt added to table salt to stop it clumping. Found only in salt and salt substitutes.
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Brine(Water, Salt), Mozzarella Full Fat Soft Cheese (Milk)(Milk, Sodium Ferrocyanide, Acid Regulator (Lactic Acid), Rennet, Starter Culture), Cream (Milk), Preservative (Sorbic Acid).
Sodium ferrocyanide is an inorganic salt where cyanide ions are tightly bound to an iron atom, forming a stable complex called a ferrocyanide.
Sodium ferrocyanide is an inorganic salt where cyanide ions are tightly bound to an iron atom, forming a stable complex called a ferrocyanide. The name contains the word cyanide, but the compound is chemically distinct from free cyanide (hydrogen cyanide or potassium cyanide). The bound form does not release cyanide under the conditions found in the human digestive system.
Acts as an anticaking agent. Its crystals coat salt particles and prevent them from absorbing moisture and sticking together. This keeps table salt free-flowing in humid conditions. E535, E536 (potassium ferrocyanide) and E538 (calcium ferrocyanide) are used interchangeably for the same purpose and share a combined maximum level.
Found almost exclusively in table salt, sea salt, and salt substitutes. Not used in processed foods directly. On a UK label it appears as E535 or sodium ferrocyanide in the ingredients list of the salt itself, not usually visible on the label of a product that merely contains salt as an ingredient.
No. Free cyanide (as in hydrogen cyanide or potassium cyanide) is acutely toxic because it is available to bind to enzymes in the body. In ferrocyanide, the cyanide ions are locked in a stable chemical bond with iron. Stomach acid is not strong enough to break this bond, so the compound passes through without releasing free cyanide. This distinction is well established in the toxicology literature and was confirmed in EFSA's 2018 re-evaluation.
Ferrocyanide is poorly absorbed from the gut, does not accumulate in tissues, and stomach acid does not release free cyanide from the iron-cyanide complex under physiological conditions.
In long-term animal studies at high doses, ferrocyanides caused kidney changes. These effects were observed at doses far above those a person would reach from salt consumption at the permitted level of 20mg/kg in salt. EFSA set a formal acceptable daily intake to maintain a safety margin between the animal effect level and typical human exposure. At the permitted food levels, EFSA concluded there was no safety concern.
Kidney toxicity was identified as the critical endpoint in animal studies. EFSA derived an ADI of 0.03 mg/kg body weight per day expressed as the ferrocyanide ion, based on these findings.
JECFA established an earlier ADI of 0 to 0.025 mg/kg body weight per day for ferrocyanides.
Available studies found no evidence that ferrocyanides damage DNA or cause cancer. EFSA's 2018 review concluded there was no genotoxic or carcinogenic concern based on the data assessed.
No genotoxicity or carcinogenicity was identified in the data reviewed by EFSA during the 2018 re-evaluation of sodium ferrocyanide.
No specific population group has been identified as needing to avoid E535 at food-additive levels. People on medically supervised very-low-sodium diets are limiting salt intake for cardiovascular reasons unrelated to E535 itself. Look for E535 or sodium ferrocyanide in the ingredients list of table salt or salt substitutes.
The word cyanide in the name causes alarm, but the chemistry here is specific: ferrocyanide is a stable iron-cyanide complex, not free cyanide. The compound is poorly absorbed, not accumulated, and has not shown genotoxic or carcinogenic properties in the studies reviewed. The one real finding is kidney damage in animals at high doses, which is why a formal ADI exists. At the quantities present in table salt and the amounts people realistically eat, the margin between the effect level in animals and human exposure is large. EFSA's 2018 re-evaluation, the most recent formal review, found no concern at current permitted levels. The science here is not particularly live or contested. It is also a useful reminder that an E number is not a processing marker in itself: table salt carries one and is not ultra-processed. Our ultra-processed foods list goes by how a food was built, not by whether it has an E number.
No. E535 is on the UK FSA's approved additives list and is permitted in salt and salt substitutes at up to 20 mg/kg.
The name includes cyanide, but E535 is a ferrocyanide, where cyanide is tightly bound to iron. The compound does not release free cyanide in the digestive system. Ferrocyanide and free cyanide are chemically distinct with very different toxicological profiles.
E535 is permitted only in table salt and salt substitutes. It is not authorised as a direct additive in processed foods. You may see it in the ingredients list of a branded salt product.
Yes. Sodium ferrocyanide is a synthetic inorganic salt. It contains no animal-derived ingredients.
Last reviewed: 20 June 2026
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