What Is Silicon Dioxide?

FDA regulations at 21 CFR 172.480 say silicon dioxide used in food is limited to an amount not exceeding 2 percent by weight of the food. The European Food Safety Authority (EFSA) says the forms of synthetic amorphous silica used as the food additive E 551 include fumed silica and hydrated silica, such as precipitated silica, silica gel and hydrous silica.

EFSA concluded in a 2024 follow-up opinion that E 551 does not raise a safety concern in all population groups at the reported uses and use levels, but said the scarcity of toxicology studies with a proper dispersion protocol creates uncertainty about the possible effects of exposure to its nanosize aggregates. In its 2018 re-evaluation, EFSA had noted that the E 551 specifications do not exclude the presence of nanoparticles and that no long-term study with nano silicon dioxide was available.

Food additive silica is not the same as silica dust. EFSA says it did not consider data on crystalline silica, which IARC classifies as a class 1 carcinogen by inhalation, because only the amorphous form of silicon dioxide is authorised as a food additive. For crystalline silica dust at work, the NIOSH Pocket Guide lists symptoms including cough, breathing difficulty, wheezing, decreased lung function and progressive respiratory symptoms of silicosis, and flags it as a potential occupational carcinogen.