Last updated: 02.03.21

COSHH Hazard Symbols and What They Mean

Many aspects of working with hazardous substances require a knowledge of COSHH classification systems. From interpreting the packaging of products used in the workplace to filling out a COSHH risk assessment form, understanding the different hazard symbols and meanings is essential in the safe use of potentially harmful substances.

A variety of jobs and workplaces involve contact with hazardous substances, such as decorating, beauty and hairdressing salons, domestic services and a wide range of medical professions. The level of risk that each industry requires is different, but in every case it is important to understand every COSHH hazard symbol and the dangers associated with that substance, ingredient or chemical.

In the last five years new regulations have been brought in across the world which have changed the system used to label toxic and harmful substances. This resource describes each of these new symbols and the hazards associated with them, along with explaining the purpose of substance warning signs.

What is COSHH?

The Control of Substances Hazardous to Health Regulations (COSHH) is a piece of health and safety legislation that was first implemented in 1998 and last updated in 2002. These regulations outline the best ways for businesses and employees to store, handle, use and dispose of hazardous substances. 

COSHH was put in place to provide a health and safety framework for using substances that pose a danger to the health of those who are exposed to them. It also implemented standardised ways of reducing the risks posed by hazardous substances and keeping exposure to an absolute minimum.

What are Hazard Symbols?

Hazard symbols (also known as hazard pictograms) are a way of alerting people to the presence of a hazardous substance with an illustration. These images are often displayed on the packaging of a substance that either is hazardous or contains a hazardous component, and illustrates how the substance could be harmful.

Original COSHH hazard symbols were black illustrations displayed inside of an orange square. However, European regulations called for new substance warning symbols to replace these in favour of a more universal set of symbols, which have been phased in to production since 2015.

New COSHH warning signs are now a black illustration within a white diamond outlined in red. They are part of the ‘Globally Harmonized System of Classification and Labelling of Chemicals’ which is used across the world to identify toxic or hazardous substances.

A Guide to COSHH Hazard Symbols

There are currently 9 official COSHH symbols in use today, although the old orange symbols can still sometimes be found on substances that were produced and packaged a while ago. Hazardous substances can be labelled with one or more of the following COSHH signs.


The symbol used to identify an explosive substance shows an exploding bomb. 

An ‘explosive’ COSHH label is used to signify that a substance has the potential to explode if placed under certain conditions. It could mean that the substance is unstable, it poses a mass explosion hazard, it poses a fire, blast or projection hazard, or that mass explosion could occur if the substance is involved in a fire.

Explosive substances are some of the most dangerous, as the consequences of an accident involving them can be catastrophic depending on their scale. If a substance or chemical is labelled with this symbol then it will have to be stored and handled carefully, away from other substances that could prompt an explosion.


The symbol used to identify a flammable substance is an illustration of a flame.

A ‘flammable’ danger symbol refers to any substance or chemical that could ignite when triggered by several different conditions. This could simply be exposure to air or a source of ignition, the substance could have a low flash point, the substance could be an ignition source or the substance could become flammable if it comes into contact with water. These substances can be solids, liquids or gases.

Flammable substances are some of the most frequently used in a variety of situations, with varying levels of danger depending on how volatile the chemical or substance is. Again, the misuse of flammable substances can have catastrophic consequences, and special equipment and storage systems are often required to prevent any accidents. 


The symbol used to identify an oxidising substance is a flame over a circle.

An ‘oxidising’ COSHH sign conveys that a substance has the potential to cause an exothermic reaction with another chemical. This reaction could result in a fire, an explosion or could increase the intensity of a fire.

Oxidising substances are quite common in most workplaces and domestic settings, as the majority of bleaches contain chemicals that are powerful oxidisers. Hairdressers in particular should be careful with how they store bleaching products, as should cleaners who purchase and store their own products. 


The symbol used to identify a corrosive substance is an illustration of two test tubes pouring a substance onto an outstretched hand and a black rectangle, both of which are shown to be reacting to the substance.

A ‘corrosive’ hazard symbol indicates that a chemical is present which may corrode living tissue or any other material if they come into contact with each other. In many cases, a corrosive substance can cause severe damage to the skin and the eyes, as well as having the potential to corrode metals and other strong materials.

Many corrosive substances are found in products such as drain cleaner and bleach, as well as being used for printing, preserving food, developing photographs and as pesticides. Those who work with corrosive chemicals must have appropriate cleaning methods and protective clothing to ensure that they do not accidentally come into contact with a substance and suffer harm.


The symbol used to identify a substance that is toxic is a skull and crossbones.

A ‘toxic’ symbol warns that a substance can cause severe damage to health, even at low levels. It can be toxic or even fatal if the substance is swallowed, inhaled or simply comes into contact with a person’s bare skin.

Substances that are toxic must be handled with extreme care, and safer alternatives should be used if possible to dramatically reduce the risk of any fatalities. Even if only a miniscule amount of a toxic substance is ingested, it can still have a severe impact on a person’s health and urgent medical advice must be sought immediately. 

Hazardous to the Environment

The symbol used to identify a substance that is hazardous to the environment is an illustration of a landscape that features a dead tree in the background and a dead fish in the foreground.

The COSHH warning sign for substances which can be hazardous to the environment signifies that they can be dangerous to one or more components of the environment if used or disposed of incorrectly. These effects can be immediate or can be slow-acting.

Pesticides, petrol, biocides and turpentine are the most commonly used substances that affect the environment and cause lasting damage. The most common environmental issue caused by hazardous substances is damage to aquatic ecosystems and toxic effects on marine life. 

Health Hazard

The symbol used to identify a substance that is a health hazard is a simple exclamation mark.

This symbol replaced previous chemical hazard symbols that meant ‘irritant’ and ‘harmful’, and is used on substances that may cause damage to health. This damage can be done if a substance is swallowed, inhaled or comes into contact with a person’s skin. 

‘Health Hazard’ substances can cause a variety of issues, including allergic reactions, respiratory problems, damage to eyesight and dizziness or drowsiness. The harm indicated by this symbol can also mean that the substance damages the earth’s ozone layer and therefore can harm the environment and general public health.

Serious Health Hazard

The symbol used to identify a substance that is a serious health hazard is an illustration of a person with white marks across their chest, representing that damage has been done to their health.

If a substance is marked with a ‘serious health hazard’ COSHH symbol then it indicates that contact with this substance could cause serious health issues or have long term effects on a person’s health. It can also mean that a substance can be fatal if it is ingested or inhaled. 

Outcomes that are classified as serious health hazards include damage to fertility, cancer, organ damage, allergies, asthma, damage to an unborn child or genetic defects. Limited or prolonged contact with a hazardous substance could result in any of these, and the health and safety measures required for these kinds of chemicals are severe.

Gas Under Pressure

The symbol used to identify a pressurised gas is a gas cylinder.

For a substance to be classified as ‘gas under pressure’, it must be in gas form and stored within a container that is pressurized. This is a potential hazard because the gas may explode if it is heated, which can cause serious danger depending on the environment.

The hazard symbol is also used for gas which is refrigerated in a container and could potentially cause cryogenic injuries and burns if it is damaged. This was the only new addition to the new substance warning symbols that has been incorporated into COSHH classifications.


What are the 9 hazard symbols?

The nine hazard symbols used to identify the kind of substances that COSHH deals with are explosive, flammable, oxidising, corrosive, acute toxicity, hazardous to the environment, health hazard, serious health hazard and gas under pressure.

What do COSHH hazard symbols mean?

Each COSHH hazard symbol means that a different hazard is present, such as a substance being corrosive, harmful to the environment or seriously harmful to health if used unsafely. They are used to alert the person interacting with the substance that a risk is present and that they need to take precautionary measures to avoid any harm to themselves, others or the environment.

Why are hazard symbols used?

A hazard symbol is used to show that a substance can be hazardous to the person using it and/or the people around them, and means that extra care should be taken to minimise the risk of any of these hazards. It is important that anyone working with dangerous substances is aware of what each of the international hazard symbols represents and can take the necessary steps to avoid each risk.


If you’re the employer or owner of a workplace or business that deals with hazardous substances, it is a legal requirement that you manage the risks associated with each of these. A key part of COSHH legislation is the completion of regular risk assessments to prevent and manage potential hazards, and understanding the symbols used on harmful substances and safety data sheets is a key part of this. 

If you’d like to refresh your knowledge of COSHH regulations and receive an in-depth description of every hazardous substance symbol, we offer an online COSHH Training program suitable for all industries and levels of responsibility.