What is it?
Boric acid is a naturally occurring weak acid of boron, water and oxygen (H3BO3). As a food additive it is a white crystalline powder. It is also used industrially as an antiseptic and pesticide.
E-numbers / Preservatives / E284
Boric acid
also: Boracic acid · orthoboric acid · hydrogen borate · E285 borax is the closely related sodium salt
A mineral acid used only as a preservative in caviar. Toxic at low doses and linked to reproductive harm, so its use is tightly restricted.
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E284
Boric acid
Boric acid accumulates in the body and causes reproductive harm in animals at doses close to typical dietary exposure from caviar.
VeganVegetarian
How common it is in UK food
1
of the 43,325 UK supermarket foods we checked declare E284 in their ingredients
That is under 0.1%, counted by its code or its name.
Counted by NutraSafe from UK supermarket ingredient lists, September 2026. How we counted
What boric acid is, what it does and where you will see it
Why it’s worth knowing. Boric acid accumulates in the body and causes reproductive harm in animals at doses close to typical dietary exposure from caviar. It is linked to testicular damage and developmental effects, and kidneys are the main target organ.
What does it do?
It inhibits mould, yeast and bacterial growth by disrupting microbial enzyme function. In caviar it slows spoilage and preserves texture. It is absorbed rapidly and completely through the gut and accumulates in the body, excreted mainly by the kidneys.
Where you will see it
Permitted only in sturgeon caviar in the UK and EU, at up to 4g per kg of product. It is not permitted in any other food categories. On a label it appears as E284 or boric acid.
What the science says
Reproductive and developmental toxicity
Animal studies show boric acid causes testicular atrophy and reduced fertility in male rats and mice at relatively low doses. Developmental studies in animals found reduced foetal weight and skeletal abnormalities at doses overlapping with estimated human dietary intake from caviar. EFSA concluded the margin of exposure from consuming caviar at the permitted level is uncomfortably narrow for reproductive endpoints.
In male rats, dietary boric acid caused testicular atrophy and impaired spermatogenesis at the lowest doses tested, establishing it as a reproductive toxin in animals.
2013AnimalEFSA ANS Panel, Scientific Opinion on the re-evaluation of boric acid (E 284) and sodium tetraborate (borax) (E 285) as food additives, EFSA Journal
Developmental studies in rats and mice showed reduced foetal weight and skeletal malformations at boric acid doses close to those that would result from consuming caviar at the permitted maximum level.
2013AnimalEFSA ANS Panel, Scientific Opinion on the re-evaluation of boric acid (E 284) and sodium tetraborate (borax) (E 285) as food additives, EFSA Journal
Kidney toxicity and accumulation
Boric acid is absorbed almost entirely from food and accumulates in the body. The kidneys are the primary target organ and show toxic changes in animal studies at repeated doses. Because the body excretes it slowly, regular consumption can lead to build-up rather than clearance.
Repeated dietary exposure to boric acid caused kidney lesions in animal studies. The kidney is the critical target organ for chronic boron toxicity.
2013AnimalEFSA ANS Panel, Scientific Opinion on the re-evaluation of boric acid (E 284) and sodium tetraborate (borax) (E 285) as food additives, EFSA Journal
EFSA could not confirm an adequate safety margin
In its 2013 re-evaluation, EFSA's food additives panel concluded it could not establish that the permitted use of boric acid in caviar provides an adequate margin of safety, particularly for reproductive effects. The panel identified a narrow gap between the dose that causes harm in animals and the dose humans could receive from caviar. EFSA did not set a numerical ADI, recommending instead that a data gap on chronic human exposure be addressed.
EFSA concluded it was unable to confirm the safety of boric acid at the permitted level in caviar and recommended that the authorisation be reviewed in light of available reproductive toxicity data.
2013Regulatory reviewEFSA ANS Panel, Scientific Opinion on the re-evaluation of boric acid (E 284) and sodium tetraborate (borax) (E 285) as food additives, EFSA Journal
Where it stands with the regulators
Approved for use in the UK and EU, but only in one specific food (sturgeon caviar). Its use in all other food categories is prohibited.
- Legal basis
- UK FSA approved-additives list and assimilated Regulation (EC) No 1333/2008 (Annex II), preservatives section. The UK FSA regulated-products register confirms E284 status as Authorised (England, Scotland and Wales) as of April 2025, with the authorisation carried over at the Brexit transition end date of 31 December 2020.
- Permitted foods
- Sturgeon caviar (caviar and other fish eggs)
- Maximum levels
- 4000mg/kg (4g per kg) in caviar
- Safe-intake limit (ADI)
- No numerical ADI set. EFSA could not establish an ADI due to concerns about the margin of safety at the permitted use level.
- History
- Boric acid has been used to preserve caviar for over a century. In 2013 EFSA re-evaluated both E284 and its related compound E285 (borax) and concluded that neither could be confirmed safe at permitted levels, particularly given reproductive and developmental toxicity data from animal studies. The permitted use has remained in place pending further review, but EFSA flagged it as a compound where the margin between the harmful dose and the intake from food is narrow. Boric acid is banned as a food additive in many countries including the US (not GRAS for food use) and Australia.
Who should be careful
People who are pregnant or planning pregnancy should be aware that boric acid accumulates in the body and is a reproductive toxin in animals. Caviar is the only permitted food source. Look for E284 or boric acid in caviar ingredient lists.
The honest read
Boric acid is one of the more contentious permitted food additives. The science is not disputed in its broad strokes: it accumulates in the body, damages the testes and developing foetuses in animal studies, and EFSA in 2013 concluded it could not confirm an adequate safety margin at the dose achievable from eating caviar. What remains uncertain is whether human dietary exposure from caviar is frequent enough or high enough to reach harmful body levels, given that caviar is a low-consumption luxury food. The concern is real and regulator-confirmed; the practical risk to most people is low because virtually no one eats caviar regularly. But the toxicological concern is not settled away: EFSA declined to set an ADI and the authorisation has been flagged for reassessment.
Common questions about boric acid
Is E284 banned in the UK?
No. E284 is permitted in the UK but only in one food: sturgeon caviar, at up to 4g per kg. It is banned or not authorised for any other food use. In the US and Australia, boric acid is not permitted as a food additive at all.
Why is boric acid only allowed in caviar?
It has been used to preserve caviar for over a century and is still permitted partly on the basis of this long traditional use. However, EFSA reviewed it in 2013 and could not confirm it is safe even in caviar, due to reproductive toxicity data from animal studies. The authorisation remains in place pending further assessment.
What foods contain E284?
In the UK and EU, only sturgeon caviar (fish eggs). It is not permitted in any other food category. If you see E284 or boric acid on any other food label, that product would be non-compliant.
Is E284 vegan?
Yes, boric acid itself is a mineral compound and contains no animal-derived ingredients. However, caviar, the only food it is permitted in, is not vegan.
Sources
- EFSA ANS Panel: Scientific Opinion on the re-evaluation of boric acid (E 284) and sodium tetraborate (borax) (E 285) as food additives, EFSA Journal 2013
- UK FSA: Approved additives and E numbers
- EU Regulation (EC) No 1333/2008 on food additives, Annex II (Preservatives)
- UK FSA Regulated Products Register: E284 Boric acid authorisation for Great Britain
Last reviewed: 20 June 2026
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