Sodium tetraborate
A boron-based preservative (borax) banned from almost all food in the UK and EU. Permitted only in sturgeon caviar at tightly controlled levels.
Borax is classified as a reproductive toxicant in the EU. Animal studies show it damages the male reproductive system and harms foetal development. It is banned from virtually all food precisely because exposure from normal food use cannot be kept below levels that cause harm in animal studies.
What is it?
Sodium tetraborate is the sodium salt of boric acid, commonly known as borax. It occurs naturally as a mineral and has been used industrially as a cleaning agent, pesticide, and preservative. As a food additive it carries the code E285.
What does it do?
Borax inhibits the growth of bacteria, yeasts and moulds, making it effective as a preservative. It lowers water activity and disrupts microbial enzyme function. In caviar, it prevents spoilage and is said to improve texture.
Where you will see it
In the UK and EU, E285 is permitted only in sturgeon caviar (fish eggs), where it may be used up to a maximum of 4g boric acid equivalent per kilogram. It is not permitted in any other food category. On a caviar label it appears as 'sodium tetraborate' or 'E285'. Borax was historically used in a wider range of foods including meat, fish and pastry in the 19th and early 20th century, but those uses were withdrawn as toxicological evidence accumulated.
What the science says
Reproductive and developmental toxicity
Animal feeding studies in rats, mice and dogs consistently show that boron compounds harm the male reproductive system, reducing fertility and causing testicular damage. High-dose exposure during pregnancy in rodents increased foetal death, reduced birth weight, and caused skeletal malformations. Based on these findings, the EU has classified boric acid and sodium tetraborate as reproductive toxicants Category 1B, meaning animal evidence strongly suggests a hazard to human reproduction.
Feeding studies in rats, mice and dogs showed adverse effects on male fertility and testicular structure at dose levels relevant to the EFSA risk assessment.
Developmental studies in rats found increased prenatal mortality, reduced foetal body weight and skeletal malformations at elevated boron intakes.
EFSA set a tolerable daily intake (TDI) for boron of 0.16mg boron per kg body weight per day and concluded that authorised use should be restricted to caviar only because dietary exposure from any broader use would approach or exceed the TDI.
EU and UK reproductive toxicant classification and REACH status
Both boric acid and sodium tetraborate are classified under EU chemical regulations as reproductive toxicants Category 1B, the category used when animal evidence is strong enough to presume a risk to human reproduction in the absence of contrary human data. Under EU REACH, disodium tetraborate was first listed as a Substance of Very High Concern (SVHC) on the Candidate List, and subsequently included in Annex XIV (the Authorisation List) of REACH, meaning it cannot be placed on the market or used in industrial or consumer applications after its sunset date unless a formal authorisation is granted by the European Commission for a specific use. The food-additive use in caviar is governed separately by food-law regulations (Regulation 1333/2008) rather than by REACH. UK REACH mirrors this position under assimilated law.
Disodium tetraborate (anhydrous) was included in Annex XIV of the REACH Regulation (the Authorisation List), requiring authorisation for industrial use after the applicable sunset date. This is a more stringent regulatory position than SVHC candidate-list inclusion alone.
Boric acid and sodium tetraborate remain on the SVHC Candidate List of substances of very high concern, primarily on the basis of reproductive toxicity Category 1B.
Where it stands with the regulators
Who should be careful
Anyone eating caviar labelled with E285 or sodium tetraborate should be aware they are consuming a reproductive toxicant at a controlled but non-zero level. Pregnant women and people trying to conceive may wish to avoid it on precautionary grounds given the animal developmental data. Look for 'E285' or 'sodium tetraborate' on the caviar ingredients list.
The honest read
The evidence base here is principally from animal studies, not from human epidemiological data, which is standard for reproductive toxicants where you cannot ethically run controlled human trials. Regulators assessed the animal findings as sufficiently strong to restrict this compound to a single niche use. The TDI is set with a safety margin applied to animal data, so a single small serving of caviar is not the same as chronic high-dose animal exposure. The restriction to caviar, rather than an outright ban, reflects the long traditional use of borax in caviar preservation and the small quantities consumed. That said, the reproductive toxicant Category 1B classification is not a minor or contested finding: it reflects a consistent pattern across multiple species and study types.
Related additives
Common questions
Is E285 banned in the UK?
Not completely. E285 is permitted in the UK but only for one specific food: sturgeon caviar, at a maximum of 4g boric acid equivalent per kilogram. It is banned from all other food categories. The US, Australia and several other countries ban it from food entirely.
Why is borax restricted to caviar?
Animal studies show borax damages the male reproductive system and harms foetal development. EFSA concluded in 2013 that dietary exposure from any broader use would exceed the tolerable daily intake, so use was limited to caviar, where consumption quantities are small and the traditional preservation benefit was judged to justify the narrow exception.
What foods contain E285?
In the UK and EU, only sturgeon caviar (fish eggs) may legally contain E285. No other food product is permitted to use it. If you see E285 or sodium tetraborate on any product other than caviar, that is a regulatory violation.
Is E285 vegan?
The additive itself is a mineral compound, but E285 is only permitted in sturgeon caviar, which is an animal product. No vegan or vegetarian food product should contain E285.
Sources
- EFSA Panel on Food Additives (ANS): Re-evaluation of boric acid (E 284) and sodium tetraborate (E 285) as food additives, EFSA Journal 11(10):3407
- UK Food Standards Agency: E285 Sodium Tetraborate (Borax) authorisation data
- UK Food Standards Agency: Approved additives and E numbers
- European Chemicals Agency (ECHA): Disodium tetraborate, anhydrous -- substance information and Annex XIV status
- European Chemicals Agency (ECHA): REACH Authorisation List (Annex XIV)
- European Chemicals Agency (ECHA): Boric acid and sodium tetraborate, SVHC candidate list entry
See this on every food you scan
NutraSafe reads the label and puts every additive into plain English, with the source, right in the app.
Get NutraSafe on the App Store