The Home Chemical Almanac · Chapter 10
Acids and alkalis
Correct as of November 2026.
If the label says "pH adjuster", "alkali", "acid" or "descaler"
Acids dissolve limescale, soap scum and rust. Alkalis cut grease, fat and burnt-on food. Both are measured on the pH scale: 7 is neutral, lower is more acidic, higher is more alkaline. At the extremes, both burn.
In Victoria, 384 people were admitted to hospital for swallowing a corrosive substance over 10 years (2007 to 2016), and 2.3% of them died. About half had a history of mental illness.
Keep acids and alkalis locked away, not under the sink. Kidsafe NSW: "Don't keep any cleaning supplies, including dishwasher detergent and dishwashing liquids, under the sink." Use safety latches, and don't rely on child-resistant caps alone. Never decant cleaners into food or drink bottles, and never mix an acid with bleach (see Chapter 4).
Ammonia is an alkali too. It's covered in Chapter 4, next to bleach.
Cheat sheet
| Chemical | Badges | Also on labels as | Worst fact | Take care if |
|---|---|---|---|---|
| Sodium hydroxide | ☠ 💧 | caustic soda, lye | 4 Queensland child deaths in 20 years, reported to the regulator | children, eyes |
| Potassium hydroxide | ☠ 💧 | caustic potash | Burnt gullets can narrow years later | children, eyes |
| Sodium carbonate | — | washing soda, soda ash | Causes serious eye damage | children, eyes |
| Sodium bicarbonate | — | bicarb soda, baking soda | In rare cases, after a big meal, it has burst stomachs | antacid overuse |
| Sodium metasilicate | ☠ | disodium metasilicate | Causes severe burns; the strongest dishwasher powders were banned in 2006 | children |
| Monoethanolamine | 🛢 💧 | MEA, ethanolamine | Reacted in 3.8% of patients tested for suspected allergy | eczema, asthma |
| Citric acid | — | E330 | Irritates eyes; etches marble | stone benches, eyes |
| Lactic acid | — | E270 | Australia classes it as causing serious eye damage | eyes, sun after skin use |
| Sulfamic acid | ☠ | amidosulfuric acid | A poison at any strength in Australia | eyes, kettles, bleach |
| Hydrochloric acid | ☠ 💧 | muriatic acid, pool acid | 60 mL of strong acid killed a woman | bleach, eyes, stone |
| Acetic acid | ☠ 🛢 💧 | vinegar, cleaning vinegar | Strong acid can perforate the oesophagus from 1 mL | children, eyes, stone |
☠ Poison schedule (Australia) · ⚠ Officially classed skin allergen · 🛢 Made from a hazardous chemical · 💧 Contaminant risk
The chemicals
Part 1: Alkalis
- Sodium hydroxide ☠ 💧
- Potassium hydroxide ☠ 💧
- Sodium carbonate
- Sodium bicarbonate
- Sodium metasilicate ☠
- Monoethanolamine 🛢 💧
Part 2: Acids
All acids etch marble, limestone and travertine, which are made of calcium carbonate. The US National Park Service warns that acidic cleaners "can be extremely damaging to acid-sensitive stones, such as marble and limestone". They can also dissolve lime-based mortar. Test a hidden spot first and rinse well.
Safer alternatives
Soap was once made at home from wood-ash lye and animal fat, and vinegar's use goes back to legend: a Babylonian courtier is said to have discovered wine about 5000 BC, which led to vinegar. Hippocrates used it on wounds. The mildest of today's choices clean well if you give them time and a scrubbing brush.
Look for these on the label:
- Citric acid or lactic acid for limescale and soap scum, in place of hydrochloric or sulfamic acid
- Table vinegar (about 4%) rather than strong cleaning vinegar, and never on stone
- Bicarb soda as a gentle scrub
- Washing soda for grease, used with gloves and kept away from eyes
- Enzyme or oxygen-bleach dishwasher products, which have a lower pH (but still keep them locked away)
Sources
Regulators and official lists
- Australian Government. Poisons Standard October 2026 (SUSMP), F2026L01327: sodium hydroxide, potassium hydroxide, alkaline salts, monoethanolamine, sulfamic acid, hydrochloric acid, acetic acid; Appendix B (sodium bicarbonate).
- TGA. Notice of interim decisions (18 Dec 2025) and final decisions (25 May 2026): ACCS #40, sodium and potassium hydroxide.
- National Drugs and Poisons Schedule Committee. Record of Reasons, 46th meeting (2006: alkaline salt dishwasher detergents) and 58th meeting (2010: lye water).
- Safe Work Australia. Hazardous Chemical Information System (HCIS): classifications for each chemical, and for ethylene oxide, carbon monoxide and acetaldehyde.
- AICIS / NICNAS. IMAP assessments: soluble silicates; ethanolamine (2013); hydrochloric acid (Tier II 2014, Tier III 2018); acetic acid (2013).
- ACCC. Analysis of consumer product related calls to the NSW Poisons Information Centre, June 2014 to May 2015 (2016).
- Queensland Injury Surveillance Unit. Injury Bulletin 87: non-medicinal ingestions (2005).
- Better Health Channel (Victorian Department of Health). Poisoning and child safety; Mould removal at home.
- Kidsafe NSW. Poisoning prevention (2017).
- FSANZ. Food Standards Code, Standard 2.10.1: vinegar.
- European Union. Regulation (EU) 2017/852 on mercury; Regulation (EU) 231/2012 food additive specifications. Minamata Convention on Mercury.
- HERA. Citric acid (2005).
- US FDA. Alpha hydroxy acids; Guidance for industry: labeling for cosmetics containing alpha hydroxy acids (2005). 21 CFR 184.1005, 184.1033, 184.1061, 182.1057.
- US EPA. Chemical Safety Alert: safe storage and handling of swimming pool chemicals (2001); Federal Register 74:26692 (L-lactic acid, 2009).
- US National Park Service. Preservation Brief 1: cleaning and water-repellent treatments for historic masonry buildings (2000).
- ILO/WHO International Chemical Safety Cards: sodium hydroxide; sulfamic acid (0328).
- HSDB (US National Library of Medicine), via PubChem: production and impurity data for each chemical.
Studies
- Rouse et al. Caustic ingestions in Victoria, 2007–2016. Intern Med J 2022;52:1185.
- Campbell D, Oates RK. Childhood poisoning: a changing profile with scope for prevention. Med J Aust 1992;156:238-240.
- Riffat F, Cheng A. Pediatric caustic ingestion: 50 consecutive cases. Dis Esophagus 2009.
- Cornish LS et al. Automatic dishwasher detergent poisoning. Aust N Z J Public Health 1996.
- Han et al. Gastric rupture after sodium bicarbonate: case reports and review. J Eat Disord 2022;10:157.
- Lessmann H et al. Skin sensitizing properties of the ethanolamines. Contact Dermatitis 2009.
- Savonius B et al. Occupational asthma caused by ethanolamines. Allergy 1994.
- Sweis IE, Cressey BC. Potential role of the common food additive manufactured citric acid in eliciting significant inflammatory reactions. Toxicol Rep 2018;5:808-812.
- Koppen et al. Descaling products and infants. Clin Toxicol 2022;60:71.
- Nuutinen M et al. Consequences of caustic ingestions in children. Acta Paediatr 1994.
- Almeida et al. Household cleaning products and SARS-CoV-2. Viruses 2022.
- Johnston CS, Gaas CA. Vinegar: medicinal uses and antiglycemic effect. MedGenMed 2006;8(2):61.
- Kilah N. Cleaning with vinegar and baking soda. The Conversation, 2024.