E-numbers / Other additives / E551
also: Silica · Amorphous silica · Synthetic amorphous silica · Fumed silica
The same mineral as sand, ground to a powder of tiny particles and added so salt, spices and powders pour instead of clumping.
Scan a barcode to check a food for silicon dioxide. NutraSafe Pro · £6.99/month · iOS
Wheat Semolina, Spices (Garlic Powder (14%), Onion Powder (8%), Black Pepper), Salt, Rosemary (2%), Anti-Caking Agent (Silicon Dioxide), Sunflower Oil
Some of the particles are nano-sized, and the legal rules for E551 do not define or limit that fraction.
399
of the 43,325 UK supermarket foods we checked declare E551 in their ingredients
That is 0.9%, counted by its code or its name.
Counted by NutraSafe from UK supermarket ingredient lists, September 2026. How we counted
Why it’s worth knowing. Some of the particles are nano-sized, and the legal rules for E551 do not define or limit that fraction. In 2018 European reviewers said the rules were not tight enough and asked for particle size to be added.
Silicon dioxide is the mineral that makes up sand and quartz. For food it is made into a powder of tiny particles that have no crystal structure, known as amorphous silica. There are several kinds, made in different ways, but all are the same mineral with a different surface.
It soaks up moisture on the surface of dry grains so they do not stick together. The tiny particles sit between the grains like ball bearings, so the powder keeps flowing. It does not dissolve in water or fat, and passes through the gut almost unchanged.
Ground spices, salt, sugar, dried milk, coffee creamers, dried egg, garlic and onion powder, icing sugar, protein powders, powdered flavourings, supplement capsules and the coating on chewing gum. UK labels call it silicon dioxide or E551.
Some of the particles in E551 as sold are smaller than 100 nanometres. The EU's legal description of E551 does not define or limit that part. In 2018 European reviewers called this a gap. In a 2024 follow-up they found the nano-sized particles have limited absorption from the gut and do not build up in the body, and asked for particle size and tighter limits on arsenic and lead to be written into the rules.
Reviewers found the legal description of E551 did not pin down particle size or rule out nanoparticles, and flagged this as a gap.
In a 2024 follow-up, reviewers raised no safety issue for any age group at reported use levels, found nano-sized particles poorly absorbed and not building up in the body, and recommended adding particle size to the rules.
Silicon dioxide is not a nutrient, and the gut takes up very little of it. What little reaches the blood is cleared by the kidneys in urine. Studies found no build-up in tissues at the amounts eaten as an additive.
Amorphous silica is very poorly absorbed in animal and human studies, and what is absorbed is quickly passed in urine. No build-up in tissue was seen at food-use amounts.
Breathing in crystalline silica dust, from cutting stone, concrete or quartz, causes silicosis and lung cancer. The silica in food is the non-crystal form and is swallowed, not breathed in. Reviewers treat the two as separate hazards, and the cancer classification for the dust does not cover the food form.
IARC classed breathed-in crystalline silica dust as causing lung cancer in humans (Group 1) in 1997, and confirmed it in 2012. The classification does not cover amorphous silica swallowed as a food additive.
Daily limit. None set.
No group is advised to avoid it. People with lung disease from crystalline silica at work sometimes ask about it, but the food form is a different, non-crystal form and is swallowed rather than breathed in. Look for silicon dioxide or E551.
Silicon dioxide barely reacts with anything, the body hardly absorbs it, and it has been in food for decades with no recorded harm at additive amounts. The open question is technical: some of its particles are nano-sized, and the legal rules do not yet define or cap that part. European reviewers looked at exactly this in 2018 and 2024 and are pushing for tighter rules, not reporting harm. In most foods it appears in, the amount is a fraction of a gram per serving.
No. Silicon dioxide is approved in the UK and is on the Food Standards Agency's list. It has not been banned or restricted.
Commercial E551 contains particles smaller than 100 nanometres, and the UK and EU rules do not define that part. European reviewers looked at this in 2018 and 2024, found the particles poorly absorbed and not building up in the body, and asked for particle size to be added to the rules. It is an open question about the rules, not a finding of harm.
Ground spices, table salt, icing sugar, dried milk, protein powders, coffee creamers, garlic and onion powder, dried egg, supplement capsules and chewing gum. It is one of the most common additives for stopping dry foods clumping.
Yes. It is a mineral, with nothing from animals.
Last reviewed: 20 June 2026
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