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Is silicon dioxide (E551) safe?
- EU: permitted — but EFSA has not set an acceptable daily intake, in 2018 or in its 2024 follow-up
- EFSA (2024): ran a nanoscale assessment and concluded E551 does not raise a safety concern at reported uses
- US & India: permitted within limits — the FDA caps anticaking use at 2% of a food's weight
- LabelCop: a medium-tier flag — the missing daily limit is the point, not a proven harm
What is silicon dioxide?
- An anti-caking agent — it stops powders clumping and keeps them free-flowing
- The food-grade form is synthetic amorphous silica, not the crystalline silica in sand and quartz
- It adds nothing nutritionally — its whole job is to make a powder behave
- Label names: silicon dioxide, silica, E551, INS 551
Which foods contain it?
- Iodised and table salt
- Instant coffee, powdered drink mixes and protein powders
- Milk powder, coffee whiteners and dessert mixes
- Grated and shredded cheese
- Powdered supplements, tablets and capsule coatings
- In India: most often in masala and spice powders, instant soup and seasoning sachets, iodised salt and drink mixes — look for INS 551 on the label
What the regulators actually say
| Regulator | Status | Reasoning |
|---|---|---|
| EFSA / European Union | Permitted — no daily limit set | EFSA's 2018 re-evaluation could not establish an acceptable daily intake, citing limited data and uncertainty about nano-sized particles. Its October 2024 follow-up again did not derive an ADI, applying a margin-of-exposure approach instead — and concluded that E551 does not raise a safety concern in any population group, including infants under 16 weeks, at reported uses. EFSA also said the EU specifications are insufficient to characterise the additive and recommended adding particle-size distribution requirements. |
| FDA (United States) | Permitted within limits | Listed as a permitted food additive under 21 CFR 172.480. Anticaking use is limited to foods where it has a demonstrated anticaking effect, at no more than 2% of the food by weight, and no more than the amount reasonably required. Also permitted as a beer stabiliser (filtered out before final processing) and as an adsorbent for certain vitamins. |
| FSSAI (India) | Permitted within limits | Permitted as an anti-caking agent (INS 551) in specified food categories under the FSS (Food Products Standards and Food Additives) Regulations, with category-specific limits — including a maximum of 2% in powdered flavouring substances. |
| WHO / JECFA | ADI "not specified" | The joint FAO/WHO expert committee gave silicon dioxide and several silicates a group ADI of "not specified" — the loosest rating it issues, used when a substance is judged to pose no hazard at the levels needed to achieve its technical effect. The rating dates from the 1980s and has not been revisited since. |
| IARC | Not a food ruling | IARC classifies inhaled crystalline silica as carcinogenic to humans (Group 1) and amorphous silica as not classifiable (Group 3). Both evaluations concern breathing dust at work, not eating the additive. |
Why do regulators disagree?
- They don't disagree on legality — every major regulator permits it. The gap is in how confidently they've cleared it
- The WHO's rating is old. "ADI not specified" was issued in the 1980s, before nanoscale toxicology existed as a field
- EFSA looked again with modern tools and couldn't produce a number. Twice — 2018 and 2024
- Why: some E551 particles and aggregates fall in the nano range, and there is no long-term study covering the full range of particle sizes a batch can contain
- The specification gap: EU rules currently set no particle-size limit for E551, so what's in the bag can vary. EFSA has recommended fixing that
- What EFSA did not say: it did not find harm. Its 2024 conclusion was no safety concern at current use levels. "No limit set" here means "we couldn't put a number on it", not "we found a problem"
The sand question
- The most common thing people ask about E551 is whether they're eating sand. They aren't
- Crystalline silica — sand, quartz, rock dust — is the form linked to lung disease and cancer when inhaled in workplaces
- Amorphous silica is the food-grade form: a different physical structure, poorly absorbed, largely passing through the gut
- Headlines that merge the two are comparing a construction-site lung hazard with a pinch of powder in your salt. Different substance form, different route, different question
- E551 is a medium-tier flag in LabelCop — not high-risk
- Reason we flag it: Europe's food safety regulator has been unable to set a safe daily limit for it (2018, and again in 2024), because of uncertainty about the very small particles it can contain — though it found no demonstrated harm at current use levels
- It is also a processing marker: a product that needs an anti-caking agent is a manufactured powder, and long additive lists usually mean ultra-processed
- A medium flag costs the product a small score penalty, not a red verdict — and you see the reason and the source. No black box
Frequently asked questions
Is silicon dioxide banned anywhere?
No. It is permitted in the EU, the US and India, and no named regulator has banned or withdrawn it. The unusual part is that EFSA has not set an acceptable daily intake for it — in 2018 the data were judged insufficient, and the October 2024 follow-up again did not derive one, while concluding E551 does not raise a safety concern at reported uses.
Is it just sand?
No. Sand and quartz are crystalline silica; the additive is synthetic amorphous silica. IARC's Group 1 carcinogen classification applies to inhaling crystalline silica dust at work. Amorphous silica sits in Group 3, not classifiable. Neither evaluation is about eating it.
What's the nanoparticle issue?
Some particles and aggregates in E551 are nano-sized, and EU specifications currently set no particle-size limit, so batches can vary. EFSA has called the specifications insufficient and recommended adding particle-size requirements. Its 2024 opinion assessed the additive at the nanoscale as well as conventionally and still found no safety concern at reported uses.
Is it safe in supplements and protein powders?
The same rules apply — it is permitted as an anti-caking agent and flow aid, at the amount needed to do the job. In the US that means no more than 2% of the product by weight for anticaking use. Supplement powders are a common place to find it because they cake badly without it.
How do I spot it?
Look for silicon dioxide, silica, E551 or INS 551 in the ingredients list, usually right at the end — or scan the label with LabelCop and it's flagged automatically, with the regulator reasoning shown.
LabelCop reads any food label you photograph and flags additives like E551 instantly — no barcode needed.
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EFSA (2018): Re-evaluation of silicon dioxide (E 551) as a food additive · EFSA (2024): Follow-up re-evaluation of E 551, including foods for infants below 16 weeks · EFSA plain-language summary of the 2024 opinion · US FDA: 21 CFR 172.480 — Silicon dioxide · WHO/JECFA: silicon dioxide, amorphous — evaluation record · FSSAI: Food Safety and Standards regulations — permitted additives · IARC Monographs Vol. 68 (1997): silica — crystalline and amorphous
Related ingredients: Titanium dioxide (E171) · Aluminium additives (E520–523, E541) · Maltodextrin
This article explains regulatory status and published scientific assessments in plain English. It is not medical advice.