E524 – Sodium hydroxide | lye uses, corrosive risk and food safety

Quick analysis summary about E524 – Sodium hydroxide food additive

Bottom line about E524

E524 is graded GREEN – SAFE at normal food-use levels after correct processing. Concentrated sodium hydroxide is highly corrosive and is not comparable to controlled use in food production.

Why this grade for E524

The main hazard is concentration-dependent corrosion. Available evidence does not identify a meaningful systemic or genotoxic concern from intended food use, although modern chronic and reproductive oral studies are limited.[1-3]

Who may want to limit or avoid E524

Most consumers need not avoid properly processed foods because of E524 alone. People following a strict low-sodium diet may still compare total sodium content.

Common uses and where E524 appears

E524 may be used to debitter olives, create pretzel crusts, alkalize cocoa, adjust acidity, and assist peeling or ingredient processing.

E524 source or origin

Sodium hydroxide is a synthetic mineral alkali commonly produced by electrolysis of purified salt brine.

Intake note for E524

JECFA assigned an ADI (Acceptable Daily Intake) not limited for intended food uses when the added dietary sodium remains acceptable. This does not mean that raw lye or concentrated solutions are safe to swallow.[3]

Is E524 banned anywhere?

E524 remains authorized in the European Union and is permitted in the United States under good manufacturing practice. No clear major food-use ban was identified in the reviewed jurisdictions, although conditions vary by food and process.

Safety grading GREEN – SAFE

Correctly used E524 presents low risk because its established hazard depends on direct contact with concentrated alkaline material. Controlled dosing, reaction, washing, and neutralization limit corrosive residues in finished food.

Study basis or key toxicological reasoning for E524

An OECD review found no valid repeated-dose oral study, so no chronic NOAEL (No Observed Adverse Effect Level) or LOAEL (Lowest Observed Adverse Effect Level) is available. Human skin irritation occurred around 0.5% to 4%, while meaningful systemic exposure was not expected under non-irritating conditions.[1] Bacterial tests and a mouse bone-marrow micronucleus test were negative. A Chinese hamster ovary test was negative without metabolic activation but positive with it. The OECD attributed the positive result to clastogenic S9 breakdown products at non-physiological pH rather than a realistic sodium hydroxide effect.[1] A Japanese compilation reported a negative Ames result and no mammalian-cell or in vivo result for sodium hydroxide.[2] In 34 volunteers, a 24-hour 4% NaOH patch and a 10-minute 0.1 mol/L test increased transepidermal water loss, confirming local irritation.[4] A mixed-substance poisoning cohort found no increased oesophageal cancer rate, but this indirect study cannot establish dietary safety.[5] A 2026 FSANZ review found no evidence that the food-additive ADI should be decreased. The main uncertainty is the limited modern chronic and reproductive oral database.[3]

Side effects of E524 – Sodium hydroxide food additive

Properly processed foods: No specific adverse effect is expected from E524 at compliant finished-food levels.
Excess residual alkalinity: Poor process control could cause an unpleasant alkaline taste and irritation of the mouth or upper digestive tract.
Sodium contribution: E524 can add sodium, although the amount remaining depends on the process and formulation.
Direct contact with lye: Concentrated material can cause severe burns to the skin, eyes, mouth, oesophagus, and stomach.
Accidental ingestion: Swallowing a concentrated solution is a medical emergency and can cause tissue death, perforation, and lasting strictures.

Should You Avoid E524 – Sodium hydroxide food additive?

Most people do not need to avoid a properly manufactured food solely because E524 appears on the label. Its controlled technological use is very different from touching or swallowing concentrated lye. Consumers managing sodium intake should judge the nutrition declaration and overall diet. Food-grade sodium hydroxide used for home pretzel, bagel, or olive preparation requires accurate dilution, protective equipment, careful handling, compliance with manufacturer instructions, and secure storage away from children.

Common uses of E524 – Sodium hydroxide food additive

Black and processed olives: Alkaline treatment helps remove bitter compounds and modify texture before washing and neutralization.
Pretzels and some bagels: Controlled surface treatment promotes browning, flavour, and crust formation.
Alkalized cocoa: Sodium hydroxide may help adjust acidity, colour, and flavour during processing.
Fruit and vegetable peeling: Dilute alkaline treatment can loosen skins before thorough washing.
pH adjustment: Manufacturers use E524 to raise pH during production of foods or ingredients.
Ingredient processing: It can modify proteins, starches, or plant materials when alkaline conditions are required.

Common names and synonyms of E524 – Sodium hydroxide food additive

Sodium hydroxide
Caustic soda
Lye
Sodium hydrate
Soda lye
INS 524

What is E524 – Sodium hydroxide food additive?

E524 is sodium hydroxide, a strong inorganic alkali with the formula NaOH. It dissolves in water into sodium and hydroxide ions, producing a high-pH solution. Manufacturers use this alkalinity to change surface browning, reduce bitterness, loosen plant skins, adjust acidity, or create processing conditions needed for particular ingredients.

Commercial sodium hydroxide is produced through the chlor-alkali process by electrolysis of purified sodium chloride brine. It may be supplied as pellets, flakes, solid material, or water-based solutions. These are physical forms of the same additive, and no officially recognized E524(i) or E524(ii) subtypes exist.

During controlled production, sodium hydroxide may react with food acids, become diluted, be removed by washing, or be neutralized before consumption. Safety therefore depends on concentration, food-grade purity, residual alkalinity, and process control. An olive-processing study found that treatment with 0.25 N sodium hydroxide for five days reduced acrylamide by more than 70% without significantly affecting firmness. This was a processing study, not a chronic safety test.[6]

Where is E524 – Sodium hydroxide food additive allowed (EU vs US)?

E524 is currently authorized in the European Union for applicable food uses and processing conditions. In the United States, sodium hydroxide is affirmed as generally recognized as safe when used as a pH-control agent and processing aid according to good manufacturing practice. Other food-regulatory systems also recognize uses of sodium hydroxide, with conditions varying by product and process.

E524 – Sodium hydroxide