E-numbers / Other additives / E521
also: Aluminium sodium sulfate · Soda alum · Sodium alum
A mineral salt used as a slow-acting leavening acid in baking powder and as a firming agent, permitted only in a narrow list of foods.
Scan a barcode to check a food for aluminium sodium sulphate. NutraSafe Pro · £3.99/month · iOS
Aluminium accumulates in the body over time and has been linked to neurotoxicity and effects on the developing brain at higher exposures.
Why it’s worth knowing. Aluminium accumulates in the body over time and has been linked to neurotoxicity and effects on the developing brain at higher exposures. The permitted food uses contribute very little, but aluminium builds up from all dietary sources combined.
Aluminium sodium sulphate is an inorganic double salt formed from aluminium sulphate and sodium sulphate. It appears as a white crystalline powder and is water-soluble. It is one of four aluminium sulphate salts permitted as food additives (E520-E523).
In baking powder, it acts as a slow-release leavening acid: it reacts with sodium bicarbonate to produce carbon dioxide gas when heated, creating a rise in batters and doughs. It also functions as a firming agent, cross-linking pectin in fruit and vegetable tissues to maintain texture during processing and cooking.
Permitted in the UK and EU only in candied, crystallised and glazed fruits (including candied cherries) and in liquid egg white preparations used to make egg foams. Actual commercial use in the UK is rare; sodium aluminium phosphate (E541) is the more common leavening acid used in baking powder. On a UK ingredient label it appears as aluminium sodium sulphate or E521.
Aluminium from all food and drink sources is absorbed in small amounts but accumulates slowly in bones, the brain and other tissues because the body clears it slowly. Animal studies show neurological effects and effects on the developing brain at doses well above typical dietary exposure. On this basis, regulators set a tolerable weekly intake covering all dietary aluminium combined, not just food additives.
EFSA set a tolerable weekly intake (TWI) of 1 mg aluminium per kilogram of body weight per week, based on neurotoxicity and neurodevelopmental effects seen in animal studies.
Animal studies identified a NOAEL of 10-42 mg aluminium per kilogram body weight per day for developmental nervous system effects in mice and rats.
JECFA set a provisional tolerable weekly intake of 2 mg aluminium per kilogram of body weight per week, also based on neurodevelopmental studies.
The two food categories where E521 is permitted (candied fruits and liquid egg white) are consumed in very small amounts. EFSA's 2018 re-evaluation estimated that exposure from these uses is most probably near the lower end of their calculated range, and concluded the additives pose no safety concern at authorised use levels. The wider concern about aluminium comes from background dietary exposure across all sources, not from E521 specifically.
EFSA concluded that aluminium sulphates E520-523 are of no safety concern in their current authorised uses and use levels, estimating that actual dietary exposure from these specific additives is probably negligible.
No concerns regarding genotoxicity, carcinogenicity or reproductive/developmental toxicity were identified at the exposure levels resulting from the authorised food uses of E520-523.
Dietary aluminium comes from many sources including drinking water, cookware, antacid medicines, and naturally occurring levels in cereals, vegetables and tea. EFSA has noted that some consumers, particularly high-end consumers, may exceed the 1 mg/kg body weight per week TWI when all sources are combined. Children are a particular concern because of their lower body weight and developing nervous systems.
A 2011 EFSA dietary exposure assessment found that mean dietary exposure to aluminium from food sources ranged from 0.2 to 1.5 mg/kg body weight per week across European countries, with some high-end consumers exceeding the TWI.
People who regularly consume large amounts of foods with aluminium-containing additives, and parents of young children, may want to be aware of cumulative aluminium from all dietary sources. E521 specifically contributes very little in practice. Look for aluminium sodium sulphate or E521 on the label; also check for other aluminium additives (E520, E522, E523, E541) and aluminium-based raising agents in the same product.
The honest picture is a split: E521 itself, in the tiny number of foods it is actually permitted in, contributes almost nothing to total aluminium intake. The regulatory concern about aluminium as a class is real and sourced: regulators set a weekly ceiling specifically because aluminium accumulates and animal studies showed neurological effects. Some European consumers exceed that ceiling from background diet (cereals, tea, cookware, water) with no additives involved at all. The additive is a footnote in that bigger picture, not the driver of it.
No. E521 is permitted in the UK and EU, but only in two specific food categories: candied and glazed fruits, and liquid egg white preparations for foams. It is not permitted in bread, standard baking powder sold to consumers, or general use.
The proposed link between dietary aluminium and Alzheimer's disease has been studied but remains unproven. Early epidemiological observations raised the question; subsequent research has not established a causal relationship. Regulatory bodies including EFSA have not classified aluminium food additives as a cause of Alzheimer's. The TWI was set based on neurodevelopmental animal data, not on Alzheimer's findings.
In the UK and EU, E521 is only permitted in candied, crystallised or glazed fruits and in liquid egg white used to make egg foams. Its actual use in UK commercial products is rare. It appears more commonly in US baking powder formulations, where it is not subject to the same use restrictions.
Yes. Aluminium sodium sulphate is a mineral salt with no animal-derived ingredients or processing. It is suitable for vegan and vegetarian diets.
Last reviewed: 20 June 2026
It's the only app that does thisUKJaneK
You Need This AppGmac2005
Best AppGK getting skinny UK App Store reviews
NutraSafe reads the label and puts every additive into plain English, with the source, right in the app.
NutraSafe Pro · £3.99/month · iOS
