The Label Rule: Silicon Dioxide

Turn over a bottle of supplements, a jar of garlic powder or a packet of powdered drink mix and you may find silicon dioxide near the end of the ingredient list. It sounds like something that belongs in a laboratory, and that is exactly why it prompts questions.

Here’s what it is, why it’s there, and what the evidence says.

What is it?

Silicon dioxide, also called silica, is a compound of silicon and oxygen. It is the main ingredient of sand and quartz, and it is one of the most common materials in the Earth’s crust. Silicon is also present in many plant foods, and silica is part of what makes up their structure.

The silicon dioxide added to food is not scooped from a beach. It is made industrially, in a form that is a very fine, fluffy, white powder. In Europe it carries the additive code E551.

Why is it there?

It is a flow agent, also called an anticaking agent. Powders pick up moisture from the air and stick together. The particles of silicon dioxide are tiny and absorb moisture, so a small amount keeps a powder loose and pourable.

You’ll find it in:

• Supplement capsules and tablets, where it helps powders flow through the machines that fill them.
• Powdered spices, salt and seasoning mixes, so they don’t turn into a block.
• Drink mixes, protein powders and powdered creamers, so they scoop and dissolve easily.

The amounts are small. In the United States, the FDA allows silicon dioxide as an anticaking agent in foods up to 2% of the food by weight. In a supplement capsule, the share is usually far smaller than that, and a single capsule is a tiny fraction of the food you eat in a day.

Enjoying this? Get one every Sunday.

One evidence-based email on healthspan and nutrition. No hype, no miracle cures.

Leave this empty

Email address

Count me in

Every Sunday. Free. Unsubscribe in one click.

What does the evidence say?

Regulators have reviewed it, more than once. The FDA permits silicon dioxide as a food additive within set limits. The European Food Safety Authority (EFSA) re-evaluated it in 2018 and again in 2024. In the 2024 review, EFSA’s panel concluded that E551 “does not raise a safety concern in all population groups at the reported uses and use levels”, including infants under 16 weeks old at current exposure levels.

There is one honest caveat: particle size. The same EFSA reports found that the particles that make up E551 are extremely small, with most only a few billionths of a metre across, and that they clump into larger aggregates. How much they clump once they are inside a food or inside your body is not well known. Because of that uncertainty and gaps in the long-term data, EFSA said it still wasn’t appropriate to set a numerical acceptable daily intake. That doesn’t mean a hazard has been found. It means the panel used a different method, comparing estimated intakes with the highest doses tested in animals, and found the intakes well below those doses.

Most of the concern comes from animal and lab studies. Studies in cells and animals using very small silica particles are where most of the worries come from. They are valuable for flagging questions, but they don’t tell us what happens at the doses people actually eat. Good long-term studies of silicon dioxide as a food additive in people are limited.

Silica packets are a different thing. The “do not eat” sachets in shoe boxes and food packages are a drying agent and are not intended to be eaten. That warning is about the packet, not about the additive in your supplement.

The Label Rule verdict

Silicon dioxide is a flow agent. It is made from one of the most common materials on Earth, used in small amounts, and reviewed by food-safety regulators in the US and Europe. For most people it is not the ingredient to worry about.

The scientific questions that remain concern its nano-sized particles and what the long-term data can show, and they are being actively studied. If you’d like to avoid it, you can: some supplements and spices are made without it, and the label will say so. If you’re choosing between two products, the more useful things to compare are usually the active ingredients, the doses, and whether anything else on the label, like added sugar or sweeteners, matters more than the flow agent at the end of the list.

This article is educational and is not medical advice. If you have allergies, a medical condition or take medicines, check with your doctor or pharmacist before changing supplements.