What is COSHH? A Complete Guide

COSHH stands for the Control of Substances Hazardous to Health Regulations 2002. It is the UK law that requires employers to prevent or control workers’ exposure to substances that can damage their health — chemicals, dusts, fumes, vapours, mists, gases and biological agents. In practice, COSHH means identifying the hazardous substances in your workplace, assessing the risk they pose, and putting controls in place so people are not harmed by them.

This guide explains what COSHH covers, what the law actually requires of employers, how to carry out a COSHH assessment, and what the hazard symbols mean.

What does COSHH stand for?

COSHH is an acronym for the Control of Substances Hazardous to Health Regulations 2002. The regulations are enforced in Great Britain by the Health and Safety Executive (HSE) and by local authorities, depending on the type of workplace.

The regulations replaced earlier versions dating back to 1988 and have been amended several times since. You can read the regulations in full on legislation.gov.uk, and the HSE publishes practical guidance at hse.gov.uk/coshh.

What are hazardous substances?

A hazardous substance is anything that can cause harm to health when people are exposed to it at work. Under COSHH, this includes:

Chemicals — cleaning products, solvents, paints, adhesives, acids and alkalis
Products containing chemicals — many everyday workplace materials
Fumes — including welding fume and exhaust fumes
Dusts — silica dust from cutting stone or concrete, wood dust, flour dust
Vapours and mists — such as those from spraying or degreasing
Gases and asphyxiating gases
Biological agents — bacteria, viruses and other micro-organisms
Germs that cause diseases such as leptospirosis or legionnaires’ disease

Substances can be hazardous even when they seem ordinary. Flour, wood dust and cleaning chemicals are all common causes of occupational ill health in the UK.

What is NOT covered by COSHH?

This is one of the most commonly misunderstood parts of the regulations. Several dangerous substances are excluded from COSHH because they have their own, separate legislation:

Asbestos — covered by the Control of Asbestos Regulations 2012 (CAR 2012)
Lead — covered by the Control of Lead at Work Regulations 2002
Radioactive substances — covered by the Ionising Radiations Regulations
Substances hazardous only because they are explosive, flammable, or at high or low temperature or pressure — these are physical hazards handled under other regulations

If your workplace involves asbestos or lead, COSHH training alone is not the right training — you need the specific training required by those regulations.

What are the health effects of hazardous substances?

Effects fall broadly into two groups:

Acute (short-term) effects appear quickly after exposure — skin irritation, burns, dizziness, nausea, breathing difficulty, or eye damage.

Chronic (long-term) effects build up over months or years and are often irreversible. These include occupational asthma, chronic obstructive pulmonary disease (COPD), dermatitis, and some occupational cancers. Silica dust and welding fume are both well-documented causes of serious long-term lung disease.

The long delay between exposure and illness is precisely why COSHH controls matter: by the time symptoms appear, the damage is often permanent.

How can I tell if a substance is hazardous?

There are three practical checks:

Look at the label. Hazardous products carry standard hazard pictograms (see below) plus hazard statements beginning with “H”.
Read the safety data sheet (SDS). Suppliers must provide one for hazardous products. Section 8 covers exposure controls and personal protection; section 11 covers toxicological information.
Consider the process, not just the product. Some hazards are created by work itself — cutting concrete creates silica dust, welding creates fume, sanding creates wood dust. None of these arrive with a label.

What do the COSHH hazard symbols mean?

The pictograms you see on containers come from the CLP Regulation (Classification, Labelling and Packaging). They are red-bordered diamonds, and there are nine of them:

Pictogram	Meaning
Exploding bomb	Explosive
Flame	Flammable
Flame over circle	Oxidising
Gas cylinder	Gas under pressure
Corrosion	Corrosive — damages skin, eyes or metals
Skull and crossbones	Acute toxicity (severe)
Exclamation mark	Irritant, skin sensitiser, acute toxicity (harmful)
Health hazard	Serious longer-term health hazards, e.g. carcinogen, respiratory sensitiser
Environment	Hazardous to the aquatic environment

Two are worth knowing well: the health hazard pictogram (the silhouette with a starburst on the chest) signals the serious chronic effects — cancer, respiratory sensitisation, reproductive toxicity. The exclamation mark signals less severe but still significant effects such as skin irritation.

What does COSHH require from employers?

The regulations place a series of duties on employers. In summary, an employer must:

Assess the risks to health from hazardous substances used or created by the work
Decide what precautions are needed — work must not begin until this is done
Prevent exposure, or where that is not reasonably practicable, adequately control it
Ensure control measures are used and maintained, and that procedures are followed
Monitor exposure where the assessment calls for it
Carry out health surveillance where the assessment shows it is necessary
Prepare plans and procedures for accidents, incidents and emergencies
Ensure employees are properly informed, trained and supervised

Note the order in duty 3. COSHH requires you to try to prevent exposure first — by removing the substance, substituting something safer, or changing the process. Personal protective equipment (PPE) is the last resort, not the first.

What is the hierarchy of control?

When exposure cannot be prevented outright, controls should be applied in this order of preference:

Elimination — stop using the substance altogether
Substitution — replace it with something less hazardous, or a less dusty form
Engineering controls — enclosure, local exhaust ventilation (LEV), on-tool extraction, water suppression
Administrative controls — safe systems of work, reducing the number of people exposed, limiting exposure time
Personal protective equipment — respirators, gloves, eye protection, coveralls

PPE sits at the bottom deliberately. It protects only the person wearing it, only while worn correctly, and fails silently when it does not fit.

How do I complete a COSHH risk assessment? (5 steps)

A COSHH assessment is not a form-filling exercise — it is a decision about how people will be protected. The HSE’s approach breaks down into five practical steps:

Step 1 — Identify the hazards

List every hazardous substance used or created by the work. Include substances produced by processes (dust, fume) as well as products bought in. Gather the safety data sheets.

Step 2 — Decide who might be harmed and how

Consider employees, contractors, cleaners, visitors, and anyone nearby. Think about how exposure happens: breathing it in, skin contact, swallowing, or injection through a wound.

Step 3 — Evaluate the risks and decide on precautions

Consider how much, how often, and for how long people are exposed. Apply the hierarchy of control above. Check whether the substance has a workplace exposure limit (see below), and whether existing controls keep exposure below it.

Step 4 — Record your findings and implement them

Write down what you found and what you have done about it. Crucially, the controls must actually be put in place, maintained and used — a documented assessment with no working controls protects nobody.

Step 5 — Review and update

Review when something changes — a new substance, a new process, a new piece of equipment — and after any incident. Reviews should also happen periodically even when nothing appears to have changed.

What is a workplace exposure limit (WEL)?

A workplace exposure limit is the maximum concentration of an airborne substance, averaged over a set period, to which workers may be exposed. WELs are published by the HSE in the guidance document EH40/2005 Workplace exposure limits, which is updated periodically.

WELs are usually expressed over two reference periods:

Long-term (8 hours) — for effects that build up over a working day
Short-term (15 minutes) — for substances that cause harm through brief, high exposure

Two important points are often missed. First, a WEL is a legal maximum, not a safe target — exposure should be reduced as far below it as is reasonably practicable. Second, not every hazardous substance has a WEL; the absence of a limit does not mean a substance is safe.

Who needs COSHH training?

Anyone who works with, or could be exposed to, hazardous substances should understand the risks and the controls that protect them. In practice this commonly includes people working in:

Construction, refurbishment and maintenance
Cleaning and facilities management
Manufacturing and engineering
Hair and beauty, and laboratories
Agriculture, catering and healthcare

Employers also have a duty under COSHH to provide suitable information, instruction and training — so managers and supervisors who plan the work need to understand it too.

Conclusion

COSHH exists because substances at work cause serious, often irreversible ill health — and because most of that harm is preventable. The regulations ask employers to do something quite logical: find out what is hazardous, work out who could be harmed, prevent exposure where you can, control it properly where you cannot, and make sure people understand what protects them.

The single most common failure is reaching for PPE first. Elimination, substitution and engineering controls come first for good reason — they protect everyone, all the time, without relying on someone remembering to wear a mask correctly.

COSHH training with Nexis CPD

Our COSHH Awareness course covers the material in this guide — hazardous substances, hazard symbols, the hierarchy of control, and how COSHH assessments work — in a short online course you can complete at your own pace.

£9 per course. CPD accredited, 100 % online, with a verifiable e-certificate issued on completion. Need more than one? Pay for 2, get 3 — any 3 courses for £18.

Please note: this is a CPD awareness course. Where your role or scheme requires a regulated qualification or licence, that must come from an approved provider — always check your employer’s or scheme’s specific requirements.

What is COSHH? A Complete Guide for UK Workplaces