Substance profile
Sodium hydroxide
Sodium hydroxide is white, orthogonal crystals and is odorless.
01 · Identification
What Sodium hydroxide is
Sodium hydroxide is white, orthogonal crystals and is odorless. Its molecular formula is HNaO and its molecular weight is 39.997 g/mol. It boils at 1388 °C, melts at 323 °C.
Under the GHS it carries the signal word Danger. It is classed as corrosives.
02 · Identifiers
Sodium hydroxide identifiers and molecular data
Sodium hydroxide CAS number and EC number
Sodium hydroxide molecular formula and molecular weight
Other names for Sodium hydroxide
- caustic soda
- lye
- NaOH
- Caustic Soda, Solid
- Soda Lye
- Sodium Hydrate
- Sodium Hydroxide (Lye)
- Sodium Hydroxide, Solid
- Sodium Hydroxide, Cresol, Xylenol
03 · GHS classification
Sodium hydroxide hazard classification
Harmonised classification under CLP Annex VI. This is the legally binding classification in the EU; other jurisdictions may differ.
Sodium hydroxide pictograms and signal word
Sodium hydroxide hazard class and category
| Hazard class | Category | From code | Pictogram |
|---|---|---|---|
| Skin corrosion/irritation GHS chapter 3.2 | Category 1A or 1B or 1C | H314 | GHS05 |
Where two values are shown with “or”, the hazard statement is shared by more than one category or by more than one class, and the code alone does not say which. H272, for example, belongs to oxidising liquids and to oxidising solids — the physical state decides. The binding answer for a specific entry is in the CLP Annex VI table itself.
Sodium hydroxide hazard statements (H-codes)
| Code | Hazard statement |
|---|---|
| H314 | Causes severe skin burns and eye damage. |
This page lists only the codes assigned to Sodium hydroxide. The full reference lives on the hazard statements hub, the precautionary statements hub and the GHS pictograms hub.
Safety Data Sheet
Getting an SDS for Sodium hydroxide
Our own Sodium hydroxide safety data sheet walks through all sixteen sections of the published data. What it is not is the document an inspector asks for: an SDS is issued for a product by its supplier, so the sheet covering the grade actually standing in your store exists only in that supplier’s version. Collecting those and keeping them current as suppliers revise them is a separate job.
04 · Precautionary statements
Sodium hydroxide precautionary statements
CLP Annex VI assigns 5 precautionary statements to Sodium hydroxide. They are grouped the way a label groups them: what to do before handling, what to do when something has already happened, how to store it and how to dispose of it.
Prevention
What to do before and during handling so the hazard never happens.
Response
What to do once exposure, spillage or fire has already happened.
Reading the notation. … is a blank the supplier fills in — not a truncated sentence.· [square brackets] mark a part printed only when it applies.
05 · Names in the regulation
Sodium hydroxide name in 23 EU languages
CLP Annex VI Part 3 is published in every language edition of the regulation, and the identification column is written out in each of them. Nothing below is translated by us: each line is the name as that edition prints it. Under Art. 18(2) the substance name from Annex VI is a lawful product identifier, so this is the wording to put on a label going to that market — and where the cell lists several designations, any one of them qualifies.
| Language | Name in CLP Annex VI Part 3 |
|---|---|
| Bulgarian български | натриев хидроксид сода каустик |
| Spanish español | Hidróxido de sodio sosa cáustica |
| Czech čeština | hydroxid sodný |
| Danish dansk | natriumhydroxid kaustisk soda |
| German Deutsch | Natriumhydroxid ÄtznatronNatronlauge |
| Estonian eesti | naatriumhüdroksiid |
| Greek ελληνικά | υδροξείδιο του νατρίου καυστική σόδα |
| English English | sodium hydroxide caustic soda |
| French français | hydroxyde de sodium soude caustique |
| Croatian hrvatski | natrijev hidroksid kaustična soda |
| Italian italiano | idrossido di sodio soda caustica |
| Latvian latviešu | nātrija hidroksīds kaustiskā soda |
| Lithuanian lietuvių | natrio hidroksidas kaustinė soda |
| Hungarian magyar | nátrium hidroxid marónátron |
| Maltese Malti | idrossidu tas-sodju soda kawstika |
| Dutch Nederlands | natriumhydroxide bijtende soda |
| Polish polski | wodorotlenek sodu soda kaustyczna |
| Portuguese português | hidróxido de sódio soda cáustica |
| Romanian română | hidroxid de sodiu sodă caustică |
| Slovak slovenčina | hydroxid sodný lúh sodný |
| Slovenian slovenščina | natrijev hidroksid kavstična soda |
| Finnish suomi | natriumhydroksidi kaustinen sooda |
| Swedish svenska | natriumhydroxid kaustiksoda |
All 23 language editions of Annex VI carry this entry. Irish is the twenty-fourth official EU language and has no line here for a different reason: no consolidated CLP text has ever been published in Irish, so there is no Irish edition of Annex VI to quote a name from. Source: consolidated CLP, CELEX 02008R1272, language editions. © European Union, https://eur-lex.europa.eu — only the electronic Official Journal of the European Union is authentic.
06 · Label elements
Sodium hydroxide GHS label elements
Everything CLP Annex VI fixes for Sodium hydroxide, laid out the way it appears on a label. The greyed lines are the parts only the supplier can fill in.
Danger
Sodium hydroxide
- Causes severe skin burns and eye damage.
- Do not breathe dust/fume/gas/mist/vapours/spray.
- Wear protective gloves/protective clothing/eye protection/face protection/hearing protection/…
- IF SWALLOWED:
- Immediately call a POISON CENTER/doctor/…
- Do NOT induce vomiting.
Supplier name, address and telephone number· Product identifier·Nominal quantity
Need this as an actual label? Open Sodium hydroxide in the GHS label constructor →
07 · Health hazards
Sodium hydroxide health hazards and exposure limits
Sodium hydroxide hazard summary
At room temperature, sodium hydroxide is a white crystalline odorless solid that absorbs moisture from the air. It is a manufactured substance. When dissolved in water or neutralized with acid it liberates substantial heat, which may be sufficient to ignite combustible materials. Sodium hydroxide is very corrosive. It is generally used as a solid or a 50% solution. Other common names include caustic soda and lye. Sodium hydroxide is used to manufacture soaps, rayon, paper, explosives, dyestuffs, and petroleum products. It is also used in processing cotton fabric, laundering and bleaching, metal cleaning and processing, oxide coating, electroplating, and electrolytic extracting. It is commonly present in commercial drain and oven cleaners.
Source: Agency for Toxic Substances and Disease Registry (ATSDR)
Sodium hydroxide occupational exposure limits
| Limit | Value | Source |
|---|---|---|
| PEL | 2.0 [mg/m3] | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
| PEL | 2 mg/m³ | Occupational Safety and Health Administration (OSHA) |
| PEL | TWA 2 mg/m3 See Appendix G | The National Institute for Occupational Safety and Health (NIOSH) |
| REL | 2 mg/m³ | Occupational Safety and Health Administration (OSHA) |
| REL | C 2 mg/m3 | The National Institute for Occupational Safety and Health (NIOSH) |
| IDLH | 10 mg/m3 [From NPG: Sodium hydroxide] (NIOSH, 2024) | CAMEO Chemicals |
| IDLH | 10 mg/m3 (NIOSH, 2024) | CAMEO Chemicals |
| IDLH | 10.0 [mg/m3] | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
These are United States values. The European Union sets its own indicative and binding limits, and the figure that applies at a given workplace is the one in the local regulation — not the one shown here.
08 · Physical and chemical properties
Sodium hydroxide properties
Every value is shown with the conditions it was measured under and the source it came from. Where sources disagree, all values are listed rather than one being picked — the difference is usually a different form of the substance, not an error.
Sodium hydroxide boiling point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Boiling point | 1388 °C (2530.4 °F) | HSDB | |
| 1390 °C (2534 °F) | NIOSH |
Sodium hydroxide melting point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Melting point | 323 °C (613.4 °F) | HSDB | |
| 318.33 °C (605 °F) | NIOSH | ||
| 317.78 °C (604 °F) | CAMEO |
Sodium hydroxide density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Density | 2.13 g/cm³ | HSDB | |
| 1.5 g/cm³ | at 20 °C | CAMEO |
Sodium hydroxide solubility
| Property | Value | Conditions | Source |
|---|---|---|---|
| Solubility | 1 g dissolves in 7.2 mL absolute alcohol, 4.2 mL methanol; also soluble in glycerol | HSDB | |
| 1 g dissolves in 0.9 mL water, 0.3 mL boiling water | HSDB | ||
| 111% | NIOSH |
Sodium hydroxide vapor pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor pressure | 0 mmHg | approx | NIOSH |
| 1.82e-21 mmHg | at 25 °C | HSDB |
Sodium hydroxide autoignition temperature
| Property | Value | Conditions | Source |
|---|---|---|---|
| Autoignition temperature | Not flammable (USCG, 1999) | CAMEO |
Sodium hydroxide lower explosive limit (LEL)
| Property | Value | Conditions | Source |
|---|---|---|---|
| Lower explosive limit (LEL) | Noncombustible Solid, but when in contact with water may generate sufficient heat to ignite combustible materials. | NIOSH |
Sodium hydroxide corrosivity
| Property | Value | Conditions | Source |
|---|---|---|---|
| Corrosivity | Very corrosive (caustic) to ... aluminum metal in presence of moisture | HSDB |
Values compiled from PubChem Laboratory Chemical Safety Summary. Temperatures converted to Fahrenheit for reference.
09 · Fire and explosion
Sodium hydroxide fire and explosion behaviour
These are descriptions rather than measured values, so they are kept out of the table above and quoted here with the source that reported them.
Sodium hydroxide fire potential
Not combustible.
Source: Hazardous Substances Data Bank (HSDB)
10 · Handling and storage
Sodium hydroxide storage and handling
Sodium hydroxide reactive group
CAMEO Chemicals places Sodium hydroxide in the reactive group Bases, Strong. Compatibility with other chemicals is worked out from the group, not from the individual substance — which is why two substances you have never seen react can still be flagged as a pair that must be separated.
A reactive group is a CAMEO Chemicals (US NOAA) grouping, not a GHS hazard class: it has no code, no category and no legal force. It is what the storage compatibility matrix on this site computes from.
Sodium hydroxide safe storage
Separated from food and feedstuffs, strong acids and metals. Store only in original container. Dry. Well closed. Store in an area without drain or sewer access.
Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Sodium hydroxide storage conditions
CONTAINERS SHOULD BE STORED IN ROOMS WITH TRAPPED FLOOR DRAINS TOWARDS WHICH FLOORS SHOULD BE SLANTED. WHERE FLOOR DRAINS ARE NOT PROVIDED, CURBS OR DRAINED GUTTER, COVERED WITH ... GRILL, SHOULD BE CONSTRUCTED @ DOOR OPENINGS.
Source: Hazardous Substances Data Bank (HSDB)
Sodium hydroxide incompatible materials
GENERATES CONSIDERABLE HEAT WHEN ... SOLN IS MIXED WITH ACID.
Source: Hazardous Substances Data Bank (HSDB)
Planning storage for a mix of chemicals? Check Sodium hydroxide in the storage compatibility matrix →
11 · Transport
Sodium hydroxide UN number and transport classification
Transport classification is a separate system from the GHS classification above. It decides how a package is marked and how a load may be carried; it does not follow from the workplace label, and the workplace label does not follow from it. The entries below are linked by CAS number, never by name.
The same CAS number is shipped under more than one UN number. Which entry applies follows from the form and the concentration of the consignment — read the proper shipping name, not the CAS.
Sodium hydroxide under UN 1823 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| SODIUM HYDROXIDE, SOLID | 8 | C6 | II | |
Source: ADR 2025, Table A of Chapter 3.2 · ECE/TRANS/352 Vol. I (UNECE). Class 8 is “Corrosive substances” (ADR 2.1.1.1).
United States · 49 CFR 172.101 Hazardous Materials Table
| Proper shipping name (column 2) | Class or division | PG | Labels (column 6) |
|---|---|---|---|
| Sodium hydroxide, solid | 8 | II | |
Source: 49 CFR 172.101 Hazardous Materials Table · eCFR, revision 2026-08-03. Class 8 is “Corrosive material” (49 CFR 173.2).
Sodium hydroxide under UN 1824 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| SODIUM HYDROXIDE SOLUTION | 8 | C5 | II | |
| SODIUM HYDROXIDE SOLUTION | 8 | C5 | III | |
Source: ADR 2025, Table A of Chapter 3.2 · ECE/TRANS/352 Vol. I (UNECE). Class 8 is “Corrosive substances” (ADR 2.1.1.1).
United States · 49 CFR 172.101 Hazardous Materials Table
| Proper shipping name (column 2) | Class or division | PG | Labels (column 6) |
|---|---|---|---|
| Sodium hydroxide solution | 8 | II | |
| Sodium hydroxide solution | 8 | III | |
Source: 49 CFR 172.101 Hazardous Materials Table · eCFR, revision 2026-08-03. Class 8 is “Corrosive material” (49 CFR 173.2).
12 · Questions
Sodium hydroxide — frequently asked questions
What is the CAS number of Sodium hydroxide?
The CAS number of Sodium hydroxide is 1310-73-2. Its EC number is 215-185-5.
What is the chemical formula of Sodium hydroxide?
The molecular formula of Sodium hydroxide is HNaO and its molecular weight is 39.997 g/mol.
What does a Sodium hydroxide label have to show?
Under CLP Annex VI the label for Sodium hydroxide carries the pictogram Corrosion and the signal word is Danger.
Is Sodium hydroxide flammable?
CLP Annex VI assigns Sodium hydroxide no flammability hazard class. That is not a statement that it cannot burn: the harmonised list only records the hazards that were assessed for it.
Is Sodium hydroxide a carcinogen?
CLP Annex VI records no harmonised carcinogenicity classification for Sodium hydroxide. Annex VI is a list of agreed classifications, not a list of substances found safe, so this is an absence of a classification rather than a clean bill of health.
What is the exposure limit for Sodium hydroxide?
The US occupational exposure limit reported for Sodium hydroxide is 2.0 [mg/m3] (Haz-Map, Information on Hazardous Chemicals and Occupational Diseases). Limits differ by country: the EU sets its own indicative and binding values, and the figure that applies at a given workplace is the one in the local regulation.
What is the boiling point of Sodium hydroxide?
The boiling point reported for Sodium hydroxide is 1388 °C (2530.4 °F) (HSDB).
What is the melting point of Sodium hydroxide?
The melting point reported for Sodium hydroxide is 323 °C (613.4 °F) (HSDB).
How should Sodium hydroxide be stored?
CONTAINERS SHOULD BE STORED IN ROOMS WITH TRAPPED FLOOR DRAINS TOWARDS WHICH FLOORS SHOULD BE SLANTED. WHERE FLOOR DRAINS ARE NOT PROVIDED, CURBS OR DRAINED GUTTER, COVERED WITH ... GRILL, SHOULD BE CONSTRUCTED @ DOOR OPENINGS. (Hazardous Substances Data Bank (HSDB))
Nearby
Substances next to Sodium hydroxide
Keep going: substances starting with S, or search the whole database by name, CAS number, pictogram or signal word.
Next