Parts Per Million (ppm)

Twenty parts per million. If you spend any time in the coeliac world, you’ll encounter this number. It’s the threshold on which gluten-free food labelling law is based in the EU, UK, USA, Australia, and most other major jurisdictions. Understanding what it means — and what it doesn’t — is worth a few minutes.

What Is the 20ppm Threshold?

Parts per million (ppm) is a measure of concentration. 20ppm of gluten means 20 milligrams of gluten per kilogram of food — or 0.002%. At that level, the food is permitted to carry a “gluten-free” label under most international food standards.

The 20ppm threshold was established based on clinical research. A landmark study by Catassi et al. (2007) — the “THRESHOLD” study — found that daily consumption of 50mg of gluten caused measurable intestinal damage in coeliacs. Working backwards from that, 10mg per day was identified as generally acceptable. Eating 500g of food per day at 20ppm delivers approximately 10mg of gluten — so the threshold is designed around realistic daily intake of GF-labelled products.

This means the 20ppm limit is not an arbitrary number. It’s a population-level safety standard derived from evidence.

However, there are nuances:

Individual variation exists. Most coeliacs tolerate food at or below 20ppm. A small number of individuals with coeliac disease have a lower threshold and react to levels that are technically within the legal limit. This is sometimes called gluten microingestion sensitivity, and it’s one reason some coeliacs choose to eat only products certified well below 20ppm, or to restrict themselves to naturally GF whole foods.

The 20ppm standard applies to the product, not a serving. If you eat multiple portions of multiple certified GF products in a day, cumulative gluten exposure could theoretically add up — though in practice this rarely reaches clinically significant levels for most coeliacs.

The Crossed Grain symbol (used in the UK and many European countries) certifies products at under 20ppm, independently verified. This remains one of the most reliable shortcuts for reliable product identification.

What This Means for You

Products certified gluten-free at under 20ppm are suitable for the vast majority of coeliacs. If you’re someone who reacts even to certified GF foods, it may be worth a conversation with your gastroenterologist about whether microingestion sensitivity could be a factor — and whether a more restricted approach is warranted.

Related in the Coeliac Alphabet: “May Contain” Labels · Zero Tolerance · Certified vs Naturally GF · back to the full A–Z.