Silicon dioxide
Anti-caking agent; nanoparticle content under EU review.
- Category
- Carriers
- Vegan
- Yes
- Vegetarian
- Yes
What it is
Silicon dioxide (E551), or synthetic amorphous silica, is an anti-caking agent. It absorbs moisture incredibly well, preventing powdered foods from turning into solid, unusable clumps. In nature, silicon dioxide is simply sand or quartz.
How it is used in food
Keeps spice mixes and instant soups free-flowing.
Commonly found in- Powdered soups and spice mixes
- Instant coffee and hot chocolate
- Salt and powdered sugar
- Dietary supplement capsules
Health and safety
The open question EFSA is chasing is whether its nano-sized fraction can accumulate.
For a long time, E551 was considered completely inert. However, the manufacturing process creates a fine powder containing a significant proportion of nanoparticles. Like Titanium dioxide (E171), these particles are so small they can cross the intestinal wall.
Potential nanoparticle toxicity
E551 contains nanoparticles that may accumulate in the body. While not currently banned, health authorities are actively reviewing evidence that these particles may cause cellular stress and genotoxicity.
Chemically inert but nanoparticles under review.
Regulatory status
| Region | Status | Notes |
|---|---|---|
| Australia & New Zealand FSANZ |
Permitted | Permitted. |
| European Union EFSA / European Commission |
Permitted | Authorised for food use under EU regulations (Annex II). |
| United States FDA (Food and Drug Administration) |
Permitted | Approved (limited to 2% of food weight). |
Identification on labels
- E-number
- E551
Also printed asSilica · Synthetic amorphous silica
Alternatives to this additive
- Rice hulls — A natural, organic alternative used to prevent clumping without the risk of synthetic nanoparticles.
How it is made
While it occurs naturally, food-grade E551 is manufactured synthetically by treating sodium silicate with an acid.
- Synthesis — Sodium silicate is reacted with an acid (like sulfuric acid) to form synthetic amorphous silica.
Worth knowing
Purified sand, in powder form so fine it coats particles.
Conclusion
EFSA and other authorities have not banned E551, but it is currently a high-anxiety ingredient. In 2018, EFSA urged manufacturers to clearly define the particle sizes, as recent animal studies suggest these nanoparticles might trigger inflammation or DNA damage.
References
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Open the appEntry last reviewed 2026-07-28.
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