Potassium hydroxide: Human health tier II assessment

24 April 2015

CAS Number: 1310-58-3

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This assessment was carried out by staff of the National Industrial Chemicals Notification and Assessment Scheme (NICNAS) using the Inventory Multi-tiered Assessment and Prioritisation (IMAP) framework.

The IMAP framework addresses the human health and environmental impacts of previously unassessed industrial chemicals listed on the Australian Inventory of Chemical Substances (the Inventory).

The framework was developed with significant input from stakeholders and provides a more rapid, flexible and transparent approach for the assessment of chemicals listed on the Inventory.

Stage One of the implementation of this framework, which lasted four years from 1 July 2012, examined 3000 chemicals meeting characteristics identified by stakeholders as needing priority assessment. This included chemicals for which NICNAS already held exposure information, chemicals identified as a concern or for which regulatory action had been taken overseas, and chemicals detected in international studies analysing chemicals present in babies’ umbilical cord blood.

Stage Two of IMAP began in July 2016. We are continuing to assess chemicals on the Inventory, including chemicals identified as a concern for which action has been taken overseas and chemicals that can be rapidly identified and assessed by using Stage One information. We are also continuing to publish information for chemicals on the Inventory that pose a low risk to human health or the environment or both. This work provides efficiencies and enables us to identify higher risk chemicals requiring assessment.

The IMAP framework is a science and risk-based model designed to align the assessment effort with the human health and environmental impacts of chemicals. It has three tiers of assessment, with the assessment effort increasing with each tier. The Tier I assessment is a high throughput approach using tabulated electronic data. The Tier II assessment is an evaluation of risk on a substance-by-substance or chemical category-by-category basis. Tier III assessments are conducted to address specific concerns that could not be resolved during the Tier II assessment.

These assessments are carried out by staff employed by the Australian Government Department of Health and the Australian Government Department of the Environment and Energy. The human health and environment risk assessments are conducted and published separately, using information available at the time, and may be undertaken at different tiers.

This chemical or group of chemicals are being assessed at Tier II because the Tier I assessment indicated that it needed further investigation.

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NICNAS has made every effort to assure the quality of information available in this report. However, before relying on it for a specific purpose, users should obtain advice relevant to their particular circumstances. This report has been prepared by NICNAS using a range of sources, including information from databases maintained by third parties, which include data supplied by industry. NICNAS has not verified and cannot guarantee the correctness of all information obtained from those databases. Reproduction or further distribution of this information may be subject to copyright protection. Use of this information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner. NICNAS does not take any responsibility whatsoever for any copyright or other infringements that may be caused by using this information.

Acronyms & Abbreviations

Chemical Identity

Synonyms caustic potash
potassium hydrate

Structural Formula Structural formula of Potassium hydroxide
Molecular Formula HKO
Molecular Weight (g/mol) 56.10
Appearance and Odour (where available) White or slightly yellow odourless lumps, rods, pellets.
SMILES O{-}.K{+}


The following Australian industrial uses were reported under previous mandatory and/or voluntary calls for information.

The chemical has reported cosmetic use.

The chemical has reported domestic uses, including in cleaning/washing agents and additives.

The chemical has reported commercial uses including:

  • in flotation agents;
  • as pH regulation agents;
  • in lubricants and additives; and
  • in bleaching agents.

The chemical has reported site-limited uses, including:

  • as a laboratory chemical;
  • in electroplating; and
  • in process regulators.

The chemical is listed on the 2006 High Volume Industrial Chemicals List (HVICL) with a total reported volume between 1,000 and 9,999 tonnes.


The following international uses have been identified through:

  • the European Union (EU) Registration, Evaluation, Authorization and Restrictions of Chemicals (REACH) dossiers;
  • the Organisation for Economic Co-operation and Development Screening Information Dataset International Assessment Report (OECD SIAR);
  • Galleria Chemica;
  • the Substances and Preparations in Nordic countries (SPIN) database;
  • the European Commission Cosmetic Ingredients and Substances (CosIng) database;
  • the United States (US) Personal Care Product Council International Nomenclature of Cosmetic Ingredients (INCI) Dictionary; and
  • the US National Library of Medicine's Hazardous Substances Data Bank (HSDB).

The chemical has reported cosmetic use as a buffering agent in, for example, moisturising creams, aftershave conditioners, hair styling products, face wash and hair removers.

The chemical has reported domestic uses including in:

  • adhesives and binding agents;
  • bleaching agents;
  • cleaning/washing agents;
  • colouring agents;
  • corrosion inhibitors;
  • fertilisers;
  • fillers;
  • foaming agents;
  • odour agents;
  • paints, lacquers and varnishes;
  • surface treatment; and
  • surface-active agents.

It also has reported domestic use as electrolytes in alkaline storage batteries.

The chemical has reported commercial uses including in:

  • absorbents and adsorbents;
  • anti-set-off and anti-adhesive agents;
  • anti-freezing agents;
  • conductive agents;
  • construction materials;
  • cutting fluids;
  • dust binding agents;
  • fixing agents;
  • flotation agents;
  • hydraulic fluids and additives;
  • impregnation materials;
  • lubricants and additives;
  • mordants for woods;
  • oxidising agents;
  • photochemicals;
  • printing inks;
  • process regulators;
  • reprographic agents;
  • welding and soldering agents;
  • softeners; and
  • solvents.

The chemical also has reported commercial use as a pH-regulation agents.

The chemical has reported site-limited use including in:

  • complexing agents;  
  • electroplating agents;
  • heat transferring agents;
  • intermediates; and
  • reducing agents.

The chemical has reported non-industrial uses, including in:

  • pharmaceuticals;
  • pesticides; and
  • food additives.


This chemical is listed in the Poisons Standard—the Standard for the Uniform Scheduling of Medicines and Poisons (SUSMP) in Schedules 5 and 6 and Appendix C (SUSMP, 2014).

Schedule 5

'POTASSIUM HYDROXIDE (excluding its salts and derivatives) in preparations containing 5 per cent or less of potassium hydroxide being:

(a) solid preparations, the pH of which in a 10 g/L aqueous solution is more than 11.5; or

(b) liquid or semi-solid preparations, the pH of which is more than 11.5 except in food additive preparations for domestic use'.

Schedule 6

'POTASSIUM HYDROXIDE (excluding its salts and derivatives) except:

(a) when included in Schedule 5;

(b) in preparations containing 5 per cent or less of potassium hydroxide being:

   (i) solid preparations, the pH of which in a 10 g/L aqueous solution is 11.5 or less; or

   (ii) liquid or semi-solid preparations, the pH of which is 11.5 or less; or

(c) liquid or semi-solid food additive preparations, the pH of which is more than 11.5, for domestic use'.

Appendix C

'POTASSIUM HYDROXIDE (excluding its salts and derivatives), in liquid or semi-solid food additive preparations, for domestic use, the pH of which is more than 11.5'.

Schedule 6 chemicals are described as 'Substances with a moderate potential for causing harm, the extent of which can be reduced through the use of distinctive packaging with strong warnings and safety directions on the label'. Schedule 6 chemicals are labelled with 'Poison' (SUSMP, 2014).

Schedule 5 chemicals are described as 'Substances with a low potential for causing harm, the extent of which can be reduced through the use of appropriate packaging with simple warnings and safety directions on the label.' Schedule 5 chemicals are labelled with 'Caution’ (SUSMP, 2014).

Appendix C chemicals are described as 'Substances, other than those included in Schedule 9, of such danger to health as to warrant prohibition of sale, supply and use' (SUSMP, 2014).


No restrictions were identified for this chemical.

Existing Work Health and Safety Controls

Hazard Classification

The chemical is classified as hazardous, with the following risk phrases for human health in the Hazardous Substances Information System (HSIS) (Safe Work Australia):

  • Xn; R22 (acute toxicity)
  • C; R35 (corrosivity)

Potassium hydroxide has a ceiling exposure standard of 2 mg/m3 (Safe Work Australia 2013).


The following exposure standards are identified (Galleria Chemica):

An exposure limit of 0.52 mg/m3 time weighted average (TWA) in different countries such as Bulgaria, Chile, Denmark, Poland and Sweden and 1–2 mg/m3 short-term exposure limit (STEL) in countries such as the United Kingdom, Spain, South Africa and Poland.

Absorbed potassium hydroxide rapidly dissociates into potassium and hydroxide ions, which enter the body's electrolyte pool. As a consequence, potential systemic effects must be discussed by considering the constituent ions (potassium ion and hydroxide ion) separately.

Both ions are normal physiological constituents. Potassium is an essential constituent of the body fluids. It is the principal intracellular cation (approximately 5.7 g/L) and it is necessary for proper functioning of neurons and muscle cells, as well as for several metabolic activities, including synthesising proteins. The hydroxide ion is a natural constituent of aqueous solutions because of the self-ionisation reaction of water.

The normal plasma concentration of potassium is approximately 140–200 mg/L. Homeostatic regulation of K+ concentration in blood is achieved primarily through renal excretion and reabsorption. Little or no toxicity is observed at potassium concentrations below 250 mg/L. Between 250 and 310 mg/L, a moderate degree of toxicity is observed, with symptoms such as lassitude, fatigue and weakness. Doses greater than 310 mg/L lead to neuromuscular paralysis and, at 390–470 mg/L, death from cardiac arrest, due to intraventricular conduction defects caused by depolarisation of cardiac muscle and subsequent increase in cardiac muscle excitability. Hyperkalaemia (elevated levels of potassium in the blood) can be produced by ingestion of 80–100 mg K+/kg bw, but cardiac effects are significant only after intravenous (i.v.) administration. The normal pH of blood is 7.35–7.45 and the absolute range of pH is 7.0–7.8. Blood pH is homeostatically regulated by a number of mechanisms, but high or repeated ingestion of potassium hydroxide or other alkaline substances can lead to alkalosis (elevated pH of the blood). Alkalosis causes hyperactivity of the central nervous system with high pH leading to prolonged muscular contractions, extreme excitability, convulsions and severe breathing difficulties (OECD, 2002).

Because the constituent ions of potassium hydroxide are naturally present in the body with effective homeostatic mechanisms working to maintain these levels, chronic systemic health effects such as repeated dose toxicity (apart from alkalosis), carcinogenicity and reproductive toxicity are not expected following exposures at non-irritating concentrations.  There are limited available data on systemic health effects of potassium hydroxide in vivo (REACH). The very limited data on potassium chloride (OECD, 2002) concludes that there is no evidence of systemic toxicity of the endogenous potassium ion. In addition, similar results were reported for sodium hydroxide (NICNAS). Potassium salts are generally considered by NICNAS to be of low concern to human health (NICNAS, 2012).


The chemical is classified as hazardous with the risk phrase 'Harmful if swallowed' (Xn; R22) in the HSIS (Safe Work Australia). The available data support this classification.

Potassium hydroxide has moderate acute toxicity based on results from three animal studies in rats following oral exposure. The median lethal dose (LD50) in rats is reported as 273–1230 mg/kg bw. The concentrations used in these tests were not reported. Observed sub-lethal effects included hyperexcitability, followed by apathy and weakness. Haemorrhaging of the stomach and intestine, and adhesions of abdominal organs (stomach, pancreas, spleen, liver and small intestine) were seen following administration of both lethal and sub-lethal doses (OECD, 2002).

In contrast, the LD50 value in rats of potassium chloride, 3000 mg/kg bw, is much higher than that of potassium hydroxide, indicating low toxicity of the potassium ion (OECD, 2002).


No data are available.


No data are available.

Observation in humans

A 2.5-year-old male suffered fatal complications from an alkaline battery foreign body in his oesophagus, resulting in corrosive burns of the oesophagus, necrosis, perforation, 'communication' (destruction of the tissue keeping the structures separate) between the oesophagus and the trachea and subsequent death (OECD, 2002).


Potassium hydroxide is corrosive to the skin, eyes and respiratory tract. It is also corrosive following ingestion. It causes deep penetrating burns and necrosis. The mechanism of injury for alkali burns is saponification of fat, which causes fatty tissue to lose its function with increased damage due to the heat of the reaction; considerable water extracted from cells due to the hygroscopic nature of alkali; and protein denaturing, permitting the hydroxide ions to penetrate deeper and produce more chemical reactions (OECD, 2002).

The chemical is a corrosive substance at concentrations of about 2 % and higher. The chemical is irritating between about 0.5 % and 2.0 %. Case reports on human accidents or intentional exposure confirm that the risk posed by potassium hydroxide for human health originates from its corrosive properties (OECD, 2002).

Skin Sensitisation

Based on the reported negative results in a guinea pig study and human experience, potassium hydroxide is not considered to be a skin sensitiser (OECD, 2002).

Observation in humans

Potassium hydroxide has been used extensively for many decades by industry and by consumers. However, skin sensitisation has never been described as secondary to skin irritation or burns. As discussed previously, both the potassium and the hydroxide constituents are ions that are naturally present in the body. For this reason, it is very unlikely that skin sensitisation would result from exposure to the chemical (OECD, 2002).

Critical Health Effects

Potassium hydroxide is corrosive to the skin, eyes, and gastrointestinal and respiratory tracts. Based on human data, concentrations of 0.5–2.0 % are irritating to the skin, while a concentration greater than 2.0 % is corrosive (OECD, 2002).

Public Risk Characterisation

Potassium hydroxide has uses in domestic and cosmetic products where it is normally used under buffering conditions that avoid extremes of pH. The main route of public exposure is expected to be contact with eyes and skin. Labelling for potassium hydroxide formulations is controlled by the Poisons Standard (SUSMP, 2014). Provided that the appropriate precautions are taken to avoid skin and eye contact or inhaling chemical aerosols, the risk from the use of domestic and cosmetic products is not considered to be unreasonable.

Occupational Risk Characterisation

During product formulation, dermal, ocular and inhalation exposure might occur, particularly where manual or open processes are used. These could include transfer and blending activities, quality control analysis, and cleaning and maintaining equipment. Worker exposure to the chemical at lower concentrations could also occur while using formulated products containing the chemical. The level and route of exposure will vary depending on the method of application and work practices employed.

Given the critical health effects, the chemical could pose an unreasonable risk to workers unless adequate control measures to minimise dermal, ocular and inhalation exposure are implemented. The chemical should be appropriately classified and labelled to ensure that a person conducting a business or undertaking (PCBU) at a workplace (such as an employer) has adequate information to determine the appropriate controls.

NICNAS Recommendation

Current risk management measures are considered adequate to protect public and workers’ health and safety, provided that all requirements are met under workplace health and safety, and poisons legislation as adopted by the relevant state or territory. No further assessment is required.

Public Health

Products containing the chemical should be labelled in accordance with state and territory legislation (SUSMP, 2014).

Work Health and Safety

The chemical is recommended for classification and labelling under the current approved criteria and adopted GHS as below. This assessment does not consider classification of physical and environmental hazards.

Hazard Approved Criteria (HSIS)a GHS Classification (HCIS)b
Acute Toxicity Harmful if swallowed (Xn; R22)* Harmful if swallowed - Cat. 4 (H302)
Irritation / Corrosivity Causes severe burns (C; R35)* Causes severe skin burns and eye damage - Cat. 1A (H314)

a Approved Criteria for Classifying Hazardous Substances [NOHSC:1008(2004)].

b Globally Harmonized System of Classification and Labelling of Chemicals (GHS) United Nations, 2009. Third Edition.

* Existing Hazard Classification. No change recommended to this classification

Advice for consumers

Products containing the chemical should be used according to the instructions on the label.

Advice for industry

Control measures

Control measures to minimise the risk from dermal or ocular exposure to the chemical should be implemented in accordance with the hierarchy of controls. Approaches to minimise risk include substitution, isolation and engineering controls. Measures required to eliminate, or minimise risk arising from storing, handling and using a hazardous chemical depend on the physical form and the manner in which the chemical is used. Examples of control measures which could minimise the risk include, but are not limited to:

  • using closed systems or isolating operations;  
  • using local exhaust ventilation to prevent the chemical from entering the breathing zone of any worker;  
  • air monitoring to ensure control measures in place are working effectively and continue to do so;
  • minimising manual processes and work tasks through automating processes;
  • work procedures that minimise splashes and spills;
  • regularly cleaning equipment and work areas; and
  • using protective equipment that is designed, constructed, and operated to ensure that the worker does not come into contact with the chemical.

Guidance on managing risks from hazardous chemicals are provided in the Managing risks of hazardous chemicals in the workplace—Code of practice available on the Safe Work Australia website.

Personal protective equipment should not solely be relied upon to control risk and should only be used when all other reasonably practicable control measures do not eliminate or sufficiently minimise risk. Guidance in selecting personal protective equipment can be obtained from Australian, Australian/New Zealand or other approved standards.

Obligations under workplace health and safety legislation

Information in this report should be taken into account to help meet obligations under workplace health and safety legislation as adopted by the relevant state or territory. This includes, but is not limited to:

  • ensuring that hazardous chemicals are correctly classified and labelled;
  • ensuring that (material) safety data sheets ((M)SDS) containing accurate information about the hazards (relating to both health hazards and physicochemical (physical) hazards) of the chemical are prepared; and
  • managing risks arising from storing, handling and using a hazardous chemical.

Your work health and safety regulator should be contacted for information on the work health and safety laws in your jurisdiction.

Information on how to prepare an (M)SDS and how to label containers of hazardous chemicals are provided in relevant codes of practice such as the Preparation of safety data sheets for hazardous chemicals—Code of practice and Labelling of workplace hazardous chemicals—Code of practice, respectively. These codes of practice are available from the Safe Work Australia website.

A review of the physical hazards of the chemical has not been undertaken as part of this assessment.


ChemIDPlus Advanced. Accessed February 2015 at

CosIng. Cosmetic Ingredients and Substances. Accessed February 2015 at

Galleria Chemica. Accessed February 2015 at

Hazardous Substances Data Bank (HSDB). National Library of Medicine. Accessed February 2015 at

National Industrial Chemicals Notification and Assessment Scheme (NICNAS) (2012). Inventory Multi-Tiered Assessment and Prioritisation Framework: Identification of chemicals of low concern to human health. Accessed March 2015 at

National Industrial Chemicals Notification and Assessment Scheme (NICNAS). Inventory Multi-tiered Assessment and Prioritisation (IMAP): Human health Tier II assessment for sodium hydroxide (CAS No. 1310-73-2). Accessed March 2015 at

NICNAS 2006. Australian High Volume Industrial Chemicals List (AHVICL). Accessed February 2015 at

OECD 2002. SIDS Initial Assessment Report (SIAR) on potassium hydroxide (1310-58-3). Accessed March 2015 at

Registration, Evaluation and Authorisation of Chemicals (REACH) Dossier. 1310-58-3. Accessed February 2015 at

Safe Work Australia (SWA) Hazardous Substances Information System (HSIS). Accessed February 2015 at

Substances in Preparations in Nordic Countries (SPIN). Accessed February 2015 at

United States (US) Personal Care Product Council International Nomenclature of Cosmetic Ingredients (INCI) dictionary. Accessed February 2015 at

Last update 24 April 2015