Aluminium hydroxide on your skin: a safety profile
Low risk(People-specific data is limited; this page draws from human adult context.) Aluminium hydroxide (ATH) is one of the most widely used flame retardants globally and is also a common antacid (Maalox, Amphojel) and vaccine adjuvant. Very low acute toxicity: oral LD50 rat >5000 mg/kg. GRAS as food-contact substance. Works as flame retardant by endothermic decomposition at 220C, releasing water. GI effects (constipation, phosphate depletion) from chronic high-dose antacid use. Aluminum absorption from oral ATH is very low (<0.1%). Vaccine adjuvant controversy is not supported by systematic evidence — WHO Global Advisory Committee on Vaccine Safety concludes aluminum adjuvants are safe.
What is aluminium hydroxide?
Also known as: ATH, Alumina trihydrate, Gibbsite, Al(OH)3.
- CAS number
- 21645-51-2
- Molecular formula
- AlH3O3
- Molecular weight
- 78.0 g/mol
- SMILES
- [OH-].[OH-].[OH-].[Al+3]
- PubChem CID
- 10176082
Risk for people
Low riskAluminium hydroxide (ATH) is one of the most widely used flame retardants globally and is also a common antacid (Maalox, Amphojel) and vaccine adjuvant. Very low acute toxicity: oral LD50 rat >5000 mg/kg. GRAS as food-contact substance. Works as flame retardant by endothermic decomposition at 220C, releasing water. GI effects (constipation, phosphate depletion) from chronic high-dose antacid use. Aluminum absorption from oral ATH is very low (<0.1%). Vaccine adjuvant controversy is not supported by systematic evidence — WHO Global Advisory Committee on Vaccine Safety concludes aluminum adjuvants are safe.
Regulatory consensus
3 regulatory and scientific bodies have classified Aluminium hydroxide. The classifications differ — that's the data.
| Agency | Year | Classification | Notes |
|---|---|---|---|
| FDA | 1973 | GRAS as food-contact substance; approved OTC antacid ingredient | |
| ECHA | 2008 | Not classified as hazardous under CLP | |
| WHO | 2012 | Approved vaccine adjuvant; safety confirmed by GACVS |
Regulators apply different standards of evidence — animal-data weighting, exposure-pattern assumptions, epidemiological power thresholds — which is why two scientific bodies can review the same data and reach different conclusions. The disagreement is the data.
Where you encounter aluminium hydroxide
- Flame Retardant
- Medicine
- Vaccines
- Water Treatment
- Cosmetics
Frequently asked questions
Why do regulators disagree about aluminium hydroxide?
Aluminium hydroxide has been classified by 3 agencies including FDA, ECHA, WHO, with differing conclusions. Regulators apply different standards of evidence (animal data weighting, exposure-pattern assumptions, epidemiological power thresholds), which is why two scientific bodies can review the same data and reach different conclusions. See the regulatory consensus table on this page for the full picture.
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Reference data, not professional advice. Aggregates publicly available regulatory and scientific data; not a substitute for veterinary, medical, legal, or regulatory advice. Why we built ALETHEIA →