Hydrated Silica
Silicon dioxide (E551) is authorized as a food additive (anticaking agent). EFSA's 2018 re-evaluation noted that available data did not raise safety concerns at current uses but flagged the need for better characterization of nano-particles.
What it is
Hydrated silicon dioxide (silica with bound water), a fine white powder.
Anticaking agent and abrasive (in toothpaste). In food, related forms (silicon dioxide / E551) act as anticaking agents.
Why it's flagged
- Nano-particle fraction characterization remains under review
What regulators actually say
"Silicon dioxide may be safely used as an anticaking agent in foods... in an amount not in excess of 2 percent by weight of the food."
"The Panel concluded that the available database did not allow an adequate assessment of the safety of silicon dioxide (E 551) as a food additive in particular as regards its nano fraction."
Regulatory status
United States — FDA
GRAS as silicon dioxide under 21 CFR 172.480 (up to 2% by weight).
European Union — EFSA
Authorized as E551 silicon dioxide; EFSA re-evaluated 2018.
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