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Glossary

What is silicon dioxide in supplements?

Written by the Full Measure editorial team, which sells supplements. Approved for publication by the Full Measure owners. Updated .

Drafted with AI assistance from the sources listed below. How we write these

Quick answer

Silicon dioxide, also called silica, is added to supplements as an anticaking and free flow agent. It keeps powders from clumping and lets them pour more freely during manufacturing. FDA permits it as an anticaking agent in food at no more than 2% of the food's weight, and the form used is synthetic amorphous silica.1,2,3

Key facts

  • FDA allows silicon dioxide as an anticaking agent at up to 2% by weight, and as an adsorbent for vitamin E acetate and panthenol in tableted foods for special dietary use.1
  • Only amorphous silica, made as fumed silica or as hydrated silica such as precipitated silica or silica gel, is authorized as the food additive in the EU.3
  • EFSA's 2024 follow up concluded that silicon dioxide raises no safety concern for any population group at reported uses and use levels, while noting uncertainty about nanosize aggregates.4
  • Silicon dioxide appears to be poorly absorbed from the gut.3

What it does in a capsule or tablet

Fine powders tend to cling together. In a 2004 laboratory study, adding colloidal silicon dioxide lowered the adhesion between particles of microcrystalline cellulose and made the powder flow more freely. FDA's name for this job is an anticaking or free flow agent: a substance added to finely powdered products to stop caking, lumping or clumping.2,5

What regulators have said

FDA lists silicon dioxide among food additives that may be used under set conditions, including the 2% limit for anticaking use.1

EFSA re-evaluated it in 2018 and again in 2024. The 2018 opinion found no indication of toxicity at reported uses but asked for clearer specifications of particle size. The 2024 opinion concluded there was no safety concern for any population group at reported uses and levels, with some uncertainty remaining about nanosize aggregates.3,4

USDA organic rules permit silicon dioxide as a defoamer, and for other uses only when organic rice hulls are not commercially available.6

Silica in food and in supplements

Silicon is part of an ordinary diet. EFSA notes that it occurs naturally in foods as silica and silicates, with estimated intakes of 20 to 50 mg of silicon a day, and an earlier EFSA panel found silicon dioxide added to food supplements at up to 1,500 mg a day to be of no safety concern.3

On a label, silicon dioxide is listed by name among the other ingredients, because it is not a dietary ingredient.7

Questions people ask

Is silicon dioxide safe in supplements?

Regulators have not found a concern at the levels used. FDA permits it as a food additive with a 2% limit for anticaking use, and EFSA's 2024 opinion found no safety concern at reported uses and levels.1,4

Is silicon dioxide the same as crystalline silica?

No. The food additive is amorphous silica, made synthetically. EFSA's review covered only that amorphous form, because only amorphous silica is authorized as a food additive in the EU.3

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Sources

  1. Code of Federal Regulations, Title 21, Section 172.480: Silicon dioxide. eCFR, current as of October 2026. Opened 2026-10-07.
  2. Jonat S, Hasenzahl S, Gray A, Schmidt PC. Mechanism of glidants: investigation of the effect of different colloidal silicon dioxide types on powder flow by atomic force and scanning electron microscopy. J Pharm Sci. 2004;93(10):2635-2644. Opened 2026-10-07.
  3. EFSA Panel on Food Additives and Nutrient Sources added to Food. Re-evaluation of silicon dioxide (E 551) as a food additive. EFSA J. 2018;16(1):e05088. Opened 2026-10-07.
  4. EFSA Panel on Food Additives and Flavourings. Re-evaluation of silicon dioxide (E 551) as a food additive in foods for infants below 16 weeks of age and follow-up of its re-evaluation as a food additive for uses in foods for all population groups. EFSA J. 2024;22(10):e8880. Opened 2026-10-07.
  5. Code of Federal Regulations, Title 21, Section 170.3: Definitions (food additives). eCFR, current as of October 2026. Opened 2026-10-07.
  6. Code of Federal Regulations, Title 7, Section 205.605: Nonagricultural substances allowed in or on processed products labeled organic or made with organic ingredients. eCFR, current as of October 2026. Opened 2026-10-07.
  7. Code of Federal Regulations, Title 21, Section 101.4: Food; designation of ingredients. eCFR, current as of October 2026. Opened 2026-10-07.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.