Magnesium hydroxide
1309-42-8 · Alcanex NHC 25 · Antacid-Laxative · Baschem 12 · CareOne Milk of Magnesia Cherry · Careone Milk of magnesia Original · Careone Milk of magnesia Original Milk of Magnesia Original · Caustic magnesite · Childrens Oral Saline Laxative · CVS Health Childrens · CVS Health Childrens Saline Laxative · CVS Magnesium Hydroxide Laxative Chew · Dulcolax Chewy Bites Assorted Fruits · Dulcolax Chewy Fruit Bites Cherry Berry · Dulcolax Liquid · Dulcolax Soft Chews Mixed Berry · Dulcolax Soft Chews Watermelon · E 528 · Equate Gentle Laxative Soft chew · Equate Kids Gentle Laxative SC · Gentle Laxative · Humco Milk Of Magnesia · Hydrate, Magnesium · Hydroxide, Magnesium · INS NO.528 · INS-528 · LAXADE · MagLax · Magmex · Magmilax Powder · MAGNALAX · Magnesii hydroxidum · Magnesium (as hydroxide) · Magnesium dihydroxide · Magnesium hydrate · Magnesium hydroxide · Magnesium hydroxide (Mg(OH)2) · Magnesium(II) hydroxide · Medibest Milk of Magnesia · Meijer Magnesium Hydroxide Laxative Soft Chew · Milk of magnesia · Milk Of Magnesia Cherry · Milk of Magnesia Concentrate · Milk Of Magnesia Liquid · Milk Of Magnesia Mint · Milk Of Magnesia Original · MiraFAST soft chews · MVT Powder · NBZ3QY004S · Phillips Fresh Mint Milk Of Magnesia · Phillips magnesia tablets · Phillips milk of magnesia liquid · Phillips Milk Of Magnesia Wild Cherry · Phillips Original Milk Of Magnesia · Premier Value Milk of Magnesia · Sunmark Milk Of Magnesia · Sunmark Milk Of Magnesia Mint · SUNMARK MILK OF MAGNESIA ORIGINAL · Walgreens Blueberry Raspberry Gentle Laxative · Walgreens Childrens · Walgreens Childrens Saline Laxative · E528 · 528 · Magnesium dihydroxide · Magnesium hydroxide · Hidroxid de magneziu · HIDRÓXIDO MAGNÉSICO · Hidróxido de magnesio · Hydroxid hořečnatý · Hydroxyde de magnésium · Idrossido di magnesio · Idrossidu tal-manjeżju · Magneesiumhüdroksiid · Magnesium hydroxide · Magnesiumhydroksidi · Magnesiumhydroxid · Magnesiumhydroxide · Magnezijev hidroksid · Magnija hidroksīds · Magnio hidroksidas · Magnézium-hidroxid · Wodorotlenek magnezu · Υδροξείδιο του μαγνησίου · Магнезиев хидроксидE number E528INS 528CAS 1309-42-8
Listed as an acidity regulator by Canada, Codex and the US.
Listed as acidity regulators (CA, US, Codex) · colours (US) · colour retention agents (Codex) · nutrient supplements (US) · processing aids (US)
- Canada: Acidity regulator — Health Canada, List of Permitted Acidity Regulators and Acid-Reacting Materials (List 10)
- United States: pH control agent — FDA, Substances Added to Food: MAGNESIUM HYDROXIDE
- United States: pH control agents — 21 CFR 184.1428, citing 21 CFR 170.3(o)(23)
- Codex Alimentarius: Acidity regulator — CXS 192-1995 Table One, INS 528
- United States: Color or coloring adjunct — FDA, Substances Added to Food: MAGNESIUM HYDROXIDE
- Codex Alimentarius: Colour retention agent — CXS 192-1995 Table One, INS 528
- United States: Nutrient supplement — FDA, Substances Added to Food: MAGNESIUM HYDROXIDE
- United States: Nutrient supplements — 21 CFR 184.1428, citing 21 CFR 170.3(o)(20)
- United States: Processing aid — FDA, Substances Added to Food: MAGNESIUM HYDROXIDE
- United States: Processing aids — 21 CFR 184.1428, citing 21 CFR 170.3(o)(24)

Magnesium hydroxide is an alkaline acidity regulator and colour retention agent, also used as a magnesium source.
Where it is and isn’t permitted
| Jurisdiction | Status | Scope and limits | Citation |
|---|---|---|---|
| Australia and New Zealand | No listed food uses foundThis site has not matched this substance to any food use on this jurisdiction’s list of authorised food additives. A food additive may be used only in foods that list names. Flavourings, enzymes, processing aids and added nutrients are regulated separately and do not appear on it. | ||
| Canada | Permitted, with conditions | highest permitted level 500 mg/kg 5 permitted uses Show every permitted use
| Health Canada, List of Permitted Acidity Regulators and Acid-Reacting Materials (List 10)and 4 further provisionsretrieved 2026-10-17 |
| European Union | Permitted, with conditions | 70 food categories highest permitted level 70,000 mg/l Show every food category
| Regulation (EC) No 1333/2008, Annex IIand 69 further provisionsretrieved 2026-10-18 |
| Great Britain | Permitted, with conditions | 68 food categories highest permitted level 70,000 mg/kg or mg/l Show every food category
| Assimilated Regulation (EC) No 1333/2008and 67 further provisionsretrieved 2026-10-18 |
| Japan | Permitted, with conditions | Designated additive: Appended Table 1, item 235, 水酸化マグネシウム (“Magnesium Hydroxide” in the unofficial English translation). …Designated additive: Appended Table 1, item 235, 水酸化マグネシウム (“Magnesium Hydroxide” in the unofficial English translation). Standards for use — Specifications and Standards for Foods, Food Additives, etc. (MHW Notification No. 370 of 1959), Part II (Food Additives), F (Standards for use): The Notification sets no standard for use (使用基準) for this additive, so it is not restricted there to particular foods or amounts. Compositional specifications for this additive, in the same Notification, are not imported and are not shown here; nor are the general rules in F 添加物一般, which apply to every additive. | Regulations for Enforcement of the Food Sanitation Act (MHW Ordinance No. 23 of 1948), Appended Table 1retrieved 2026-10-18 |
| South Korea | Permitted, with conditions | Designated food additive: Standards and Specifications for Food Additives, Part III, 1. …Designated food additive: Standards and Specifications for Food Additives, Part III, 1. 일반식품첨가물 (general food additives), 수산화마그네슘 (“Magnesium Hydroxide”, the English the Code prints beside it); the Code marks it as also usable as a nutrient fortifier; 3. 영양강화제 (nutrient fortifiers), 수산화마그네슘; nutrient: 마그네슘 (Mg); the Code marks it as also usable as a general food additive. Main use (주용도) of 수산화마그네슘: 산도조절제. Standard for use (사용기준) of 수산화마그네슘: (1) [to be used under the general standard for use in II. 2. 1), the minimum amount that achieves the technical effect, with no limit set for this additive in particular] “II. 2. 1)의 규정에 따라 사용하여야 한다.” The Korean is the standard as published. There is no official English translation of the current Code (the English version on MFDS’s website is the 2020 edition and has no legal effect); the English in square brackets is this site’s description of what each sentence does, not a translation of the foods or the levels. Compositional specifications (Part IV) are not imported, nor are the general standards in Part II, which apply to every additive. | Standards and Specifications for Food Additives (식품첨가물의 기준 및 규격), MFDS Notification, Part III (Standards for use, by item)retrieved 2026-10-18 |
| United States | Permitted | 21 CFR 184.1428retrieved 2026-10-17 | |
| Codex Alimentarius | Permitted, with conditions | 9 food categories no numerical limit (good manufacturing practice) Show every food category and its notes
| CXS 192-1995 Table Three, INS 528and 9 further provisionsretrieved 2026-09-07 |
How much is permitted
A listing usually limits the quantity as well as the food. Only one of the forms that takes is a figure: quantum satis and good manufacturing practice permit the amount the technological effect requires and no more, which is a limit rather than the absence of one. Figures below are the range across every food category this page is listed in, and categories differ between regulators — see how much is permitted.
| Canada | 500 mg/kg | 1 numeric limit, 4 GMP |
|---|---|---|
| European Union | 70,000 mg/kg | 1 numeric limit, 46 several limits, 1 quantum satis, 22 no quantity stated |
| Great Britain | 70,000 mg/kg | 1 numeric limit, 67 quantum satis |
| Japan | — | 1 no quantity stated |
| South Korea | — | 1 no quantity stated |
| United States | — | 1 no quantity stated |
| Codex Alimentarius | — | 10 GMP |
What it is made from
Precipitated from seawater or magnesium salt solutions with an alkali.
- Vegan
- Vegetarian
Compare other additives on the dietary indexes.
- CAS registry number
- 1309-42-8
- InChIKey
- VTHJTEIRLNZDEV-UHFFFAOYSA-L
- PubChem
- CID 73981
The two specifications, compared
The European Union sets identity and purity by regulation; JECFA publishes its own through FAO, advisory until a country adopts it. Both documents are below in full. These are the parameters each puts a number on.
| Parameter | European Union | JECFA |
|---|---|---|
| Assay | no less than 95 % | no less than 95 % |
| Loss on drying | no more than 2 % | no more than 2 % |
| Lead | no more than 2 mg/kg | no more than 2 mg/kg |
| Arsenic | no more than 3 mg/kg | — |
The two documents state the same figures for every parameter compared here.
How the EU defines it
The legal specification an additive must meet to be sold as this E number in the EU — what it is, how it may be made, and the purity it must reach. From Commission Regulation (EU) No 231/2012.
E 528 Magnesium hydroxide
Assay, identification and purity criteria
Description and assay
- Chemical name
- Magnesium hydroxide
- Chemical formula
- Mg(OH)₂
- Molecular weight
- 58,32
- Assay
- Content not less than 95,0 % on the anhydrous basis
- Description
- Odourless, white bulky powder
Identification
- Test for magnesium
- Passes test
- Test for alkali
- Passes test
- Solubility
- Practically insoluble in water and in ethanol
Purity criteria
- Loss on drying
- Not more than 2,0 % (105 °C, 2 hours)
- Loss on ignition
- Not more than 33 % (800 °C to constant weight)
- Calcium oxide
- Not more than 1,5 %
- Arsenic
- Not more than 3 mg/kg
- Lead
- Not more than 2 mg/kg
How JECFA defines it
The international specification for identity and purity, prepared by the Joint FAO/WHO Expert Committee on Food Additives and published by FAO. It is a different document from any above, written by a different body and revised on its own cycle; it is advisory, and a country adopts it or does not.
INS 528 Magnesium Hydroxide
Synonyms: INS No. 528
Assay, identification and purity criteria
Description and assay
- Specification history
- Prepared at the 19th JECFA (1975), published in NMRS 55B (1976) and in FNP 52 (1992). Metals and arsenic specifications revised at the 59th JECFA (2002). An ADI not limited' was established at the 9th JECFA (1965)
- Chemical names
- Magnesium hydroxide
- C.A.S. number
- 1309-42-8
- Chemical formula
- Mg(OH) 2
- Formula weight
- 58.32
- Assay
- Not less than 95.0%
- DESCRIPTION
- Odourless, white bulky powder
- FUNCTIONAL USES
- Alkali, colour adjunct
- METHOD OF ASSAY
- accurately weighed, into a conical flask. Add 25 ml of 1 N sulfuric acid and, after solution is complete, add methyl red TS and titrate the excess acid with 1 N sodium hydroxide. Subtract from the volume of 1 N sulfuric acid consumed in the assay the volume of 1 N sulfuric acid corresponding to the weight of CaO in the sample taken for the assay using as a factor 28.04 mg of CaO for each ml of 1 N sulfuric acid. Each ml of 1 N sulfuric acid used to neutralize the magnesium hydroxide is equivalent to 29.16 mg of Mg(OH) 2 .
Identification
- Solubility (Vol. 4)
- Practically insoluble in water and in ethanol
- Test for alkali
- The sample is alkaline to moistened litmus paper
- Test for magnesium (Vol. 4)
- Passes test
Purity criteria
- Loss on drying (Vol. 4)
- Not more than 2% (105 o , 2 h)
- Loss on ignition (Vol. 4)
- Not more than 30 - 33% (approx. 800 o to constant weight)
- Alkalis (free) and soluble salts
- Boil 2 g of the sample with 100 ml of water for 5 min in a covered beaker and filter while hot. Add methyl red TS and titrate 50 ml of the cooled filtrate with 0.1 N sulfuric acid. Not more than 2 ml of the acid is required to reach the endpoint. Evaporate 25 ml of the filtrate to dryness and dry at 105 o for 3 h. Not more than 10 mg of residue remains.
- Calcium oxide
- Not more than 1.5% Dissolve about 500 mg of the sample, accurately weighed, in a mixture of 3 ml of concentrated sulfuric acid and 22 ml of water. Add 50 ml of ethanol and allow the mixture to stand overnight. If crystals of magnesium sulfate separate, warm the mixture to about 50 o to dissolve. Filter through a Gooch crucible containing an asbestos mat previously washed with dilute sulfuric acid TS, water, and ethanol and ignited and weighed. Wash the crystals on the mat several times with a mixture of 3 volumes of ethanol and 1 volume of water. Ignite the crucible and contents at a dull red heat, cool and weigh. The weight of calcium sulfate obtained, multiplied by 0.4119, gives the equivalent of calcium oxide in the sample taken for the test.
- Lead (Vol. 4)
- Not more than 2 mg/kg Determine using an atomic absorption technique appropriate to the specified level. The selection of sample size and method of sample preparation may be based on the principles of the method described in Volume 4, “Instrumental Methods.” Transfer about 400 mg of the sample, previously dried at 105 o for 2 h and
Authorised in other additives, enzymes, flavourings and nutrients
These authorisations are not for use in food. They let this substance be used inside another additive, a food enzyme, a flavouring or a nutrient preparation — often as a carrier — and it reaches food only as part of that product. Annex III to Regulation (EC) No 1333/2008.
| Part | May be used in | Maximum level | Citation |
|---|---|---|---|
| Annex III, Part 2: Food additives other than carriers in food additives | All food additive preparationsAuthorised as a member of Table 1 of Part 6, listed as "Table 1" Note (1): Except enzymes authorised as food additives. | quantum satis | Regulation (EC) No 1333/2008, Annex III, Part 2, via Table 1 of Part 6 |
| Annex III, Part 3: Food additives including carriers in food enzymes | Food enzymesCan be used as a carrier: Yes Note (1): Including enzymes authorised as food additives. | In enzyme preparation: quantum satis In final food except beverages: quantum satis In beverages: quantum satis | Regulation (EC) No 1333/2008, Annex III, Part 3 |
| Annex III, Part 4: Food additives including carriers in food flavourings | All flavouringsAuthorised as a member of Table 1 of Part 6, listed as "Table 1" | quantum satis | Regulation (EC) No 1333/2008, Annex III, Part 4, via Table 1 of Part 6 |
| Annex III, Part 5, Section A: Food additives added in nutrients except in nutrients intended to be used in foodstuffs listed in Part E, point 01.10, of Annex II and foodstuffs for infants and young children listed in Part E, point 13.1, of Annex II | All nutrients | quantum satis | Regulation (EC) No 1333/2008, Annex III, Part 5, Section A |
Every name it appears under
84 recorded names. A label may use any of them.
E number
- E528
INS number
- 528
CAS registry number
- 1309-42-8
As it appears in regulation
- Magnesium hydroxide
Other names
- Alcanex NHC 25
- Antacid-Laxative
- Baschem 12
- CareOne Milk of Magnesia Cherry
- Careone Milk of magnesia Original
- Careone Milk of magnesia Original Milk of Magnesia Original
- Caustic magnesite
- Childrens Oral Saline Laxative
- CVS Health Childrens
- CVS Health Childrens Saline Laxative
- CVS Magnesium Hydroxide Laxative Chew
- Dulcolax Chewy Bites Assorted Fruits
- Dulcolax Chewy Fruit Bites Cherry Berry
- Dulcolax Liquid
- Dulcolax Soft Chews Mixed Berry
- Dulcolax Soft Chews Watermelon
- E 528
- Equate Gentle Laxative Soft chew
- Equate Kids Gentle Laxative SC
- Gentle Laxative
- Humco Milk Of Magnesia
- Hydrate, Magnesium
- Hydroxide, Magnesium
- INS NO.528
- INS-528
- LAXADE
- MagLax
- Magmex
- Magmilax Powder
- MAGNALAX
- Magnesii hydroxidum
- Magnesium (as hydroxide)
- Magnesium dihydroxide
- Magnesium hydrate
- Magnesium hydroxide
- Magnesium hydroxide (Mg(OH)2)
- Magnesium(II) hydroxide
- Medibest Milk of Magnesia
- Meijer Magnesium Hydroxide Laxative Soft Chew
- Milk of magnesia
- Milk Of Magnesia Cherry
- Milk of Magnesia Concentrate
- Milk Of Magnesia Liquid
- Milk Of Magnesia Mint
- Milk Of Magnesia Original
- MiraFAST soft chews
- MVT Powder
- NBZ3QY004S
- Phillips Fresh Mint Milk Of Magnesia
- Phillips magnesia tablets
- Phillips milk of magnesia liquid
- Phillips Milk Of Magnesia Wild Cherry
- Phillips Original Milk Of Magnesia
- Premier Value Milk of Magnesia
- Sunmark Milk Of Magnesia
- Sunmark Milk Of Magnesia Mint
- SUNMARK MILK OF MAGNESIA ORIGINAL
- Walgreens Blueberry Raspberry Gentle Laxative
- Walgreens Childrens
- Walgreens Childrens Saline Laxative
Systematic names
- Magnesium dihydroxide
Hazard reference values
| Type | Value | Population | Assessed by | Opinion |
|---|---|---|---|---|
| ADI | not limited | — | JECFA | 1965 |
Evidence and how bodies read it
Studies, and the differing conclusions regulators drew from them, are curated rather than machine-read, and none has been written for this substance yet.
Common questions
Assembled from what is above, in the words the questions are usually asked in. Each answer is the same statement the relevant section makes, with the same citations behind it.
- What is E 528?
- E 528 is Magnesium hydroxide. Magnesium hydroxide is an alkaline acidity regulator and colour retention agent, also used as a magnesium source.
- What is Magnesium hydroxide used for in food?
- It is listed as an acidity regulator — the role Canada, Codex and the US assign it. This page shows every function each regulator records, with the citation for each.
- Where is Magnesium hydroxide permitted?
- Of the seven regulators this site reads, Canada, the EU, Great Britain, Japan, South Korea, the US and the Codex standard permit it. Each permission is for named foods at named levels, not a blanket one; the table on this page gives them with citations.
- Is Magnesium hydroxide vegan?
- Yes. Magnesium hydroxide is not derived from animals, and is suitable for vegetarians. This page says what it is made from and how.
Sources for this page
- ca retrieved 2026-10-17
- eu retrieved 2026-10-18
- gb retrieved 2026-10-18
- jp retrieved 2026-10-18
- kr retrieved 2026-10-18
- ecfr retrieved 2026-10-17
- gsfa retrieved 2026-09-07
- euspecs retrieved 2026-10-18
- jecfaspecs retrieved 2026-09-23
Full licence terms and publisher details on Sources. How this page is built and updated: Method.
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