E551 - Silicon dioxide

At a glance

• What it is: Food‑grade, synthetic “amorphous” silica, not the same as crystalline quartz found in sand.
• What it does: Keeps powders from clumping (anti‑caking agent) and carries flavors, colors, or nutrients.
• Where it appears: Seasonings, salt, dry mixes, instant products, and many food supplements.
• Typical amount: Very small—often up to 2% of the food in the U.S.
• Look for it on labels as: Silicon dioxide, silica, E551, or SiO2.

Why is Silicon dioxide added to food?

Manufacturers add silicon dioxide to stop powders from clumping. Its tiny particles have a high surface area and soak up moisture, so salt, spices, mixes, and supplements pour and blend evenly. In the U.S., it is permitted as an anti‑caking agent in amounts not exceeding 2 percent by weight of the finished food.¹

What foods contain Silicon dioxide?

You are most likely to find E551 in dry, powdery foods. Examples include table salt and seasoning blends, soup and sauce mixes, instant drink powders, and food supplements in powder or capsule form.²

What can replace Silicon dioxide?

Several additives can do a similar job, depending on the recipe:

• Mineral anti‑caking agents such as calcium silicate, tricalcium phosphate, and talc
• Fibers and starches like cellulose
• In supplements and tablets, flow agents such as magnesium stearate

How is Silicon dioxide made?

Food‑grade silicon dioxide is a synthetic, amorphous material. It is made by:

• Precipitation: reacting sodium silicate with acid to form “precipitated silica”
• Forming silica gel: a hydrated form made from sodium silicate and acid
• Vapor‑phase (fumed) process: flame hydrolysis of silicon compounds to make very fine “fumed silica” These forms meet identity and purity rules in U.S. regulations for food use.¹

Is Silicon dioxide safe to eat?

Regulators have reviewed silicon dioxide and allow it in foods at current use levels. The European Food Safety Authority (EFSA) concluded that silicon dioxide (E551) is safe at reported uses and levels. EFSA also noted that most food‑grade material is amorphous and recommended tighter specifications on particle size for future clarity.² In the U.S., its permitted use level (up to 2%) is set in federal regulations.¹

Does Silicon dioxide have any benefits?

Silicon dioxide does not add taste or nutrition. Its benefit is practical: it keeps powders free‑flowing, improves mixing, and helps ensure even dosing in packets, spice shakers, and supplement capsules. As a carrier, it also helps disperse flavors and colors evenly in a blend.

Who should avoid Silicon dioxide?

Most people do not need to avoid dietary silicon dioxide at typical levels used in food. The main safety concern you may hear about involves breathing crystalline silica dust at work, which is a different form (crystalline, not the amorphous food‑grade type) and relates to air exposure, not eating.³ If your healthcare provider recommends limiting food additives in general, follow their advice.

Myths & facts

• Myth: “It’s just sand.” Fact: Food‑grade silicon dioxide is amorphous silica, not crystalline quartz.
• Myth: “It builds up in the body.” Fact: It is used in tiny amounts to control clumping and does not act as a nutrient or preservative.
• Myth: “Nano-silica in food is unregulated.” Fact: Food authorities review particle size and safety data as part of their assessments and specifications.

Silicon dioxide in branded foods

You will often see E551 on labels for spice blends, table salt, instant drink mixes, dry soup or sauce packets, and many powdered or encapsulated supplements. Look for the names “silicon dioxide,” “silica,” or “E551” in the ingredient list. Amounts are small and may not be shown as a percentage.

References

Footnotes

1. 21 CFR 172.480 — Silicon dioxide. U.S. Food and Drug Administration (eCFR). https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-172/subpart-D/section-172.480 ↩ ↩² ↩³

2. Re-evaluation of silicon dioxide (E 551) as a food additive — European Food Safety Authority (EFSA Journal 2018;16(1):5088). https://efsa.onlinelibrary.wiley.com/doi/10.2903/j.efsa.2018.5088 ↩ ↩²

3. Crystalline Silica — Health Effects. National Institute for Occupational Safety and Health (NIOSH), CDC. https://www.cdc.gov/niosh/topics/silica/default.html ↩