COSHH stands for the Control of Substances Hazardous to Health. It is a set of UK regulations that require employers to protect workers from health risks caused by hazardous substances in the workplace. The regulations came into force on 21 November 2002 under the Health and Safety at Work etc. Act 1974 and are enforced by the Health and Safety Executive (HSE).
What COSHH Covers
COSHH applies to a broad range of substances that can harm your health at work. These include chemicals, products containing chemicals, fumes, dusts, vapours, mists, gases, asphyxiating gases, nanotechnology particles, and biological agents such as bacteria and viruses. In practical terms, this means everything from cleaning products and paint to welding fumes, flour dust, and laboratory cultures falls under COSHH.
A few hazardous substances are serious enough to have their own separate regulations. Asbestos, lead, and radioactive materials are each covered by dedicated legislation with stricter requirements, so they sit outside COSHH even though they are clearly dangerous.
How Hazardous Substances Are Labelled
Products covered by COSHH carry standardised warning symbols: a pictogram on a white background inside a red diamond border. Each symbol represents a specific type of hazard. A skull and crossbones indicates acute toxicity (fatal or toxic doses). A corrosion symbol warns of burns to skin or eyes. The “health hazard” silhouette of a person marks longer-term dangers like cancer risk, reproductive toxicity, or organ damage. A flame means the substance is flammable, and an exclamation mark signals irritants or lower-level toxic effects.
If you work with any product carrying these symbols, COSHH almost certainly applies. The product’s safety data sheet will give you the specific hazards and handling instructions your employer needs for their risk assessment.
What Employers Must Do
Under COSHH, employers carry the legal burden of keeping workers safe from hazardous substances. The core obligation is to carry out a risk assessment: identify which hazardous substances are present, determine who might be exposed and how, evaluate the level of risk, and decide what controls to put in place. If your business has five or more employees, this assessment must be recorded in writing. Even smaller businesses benefit from documenting it.
The HSE sets out eight principles of good control practice that employers must follow. These principles work together rather than in a strict ranking, but there is a logical order to them:
- Minimise emission, release, and spread of hazardous substances
- Consider all routes of exposure, including breathing it in, skin contact, and swallowing
- Choose control measures proportionate to the risk
- Choose effective and reliable control options
- Use personal protective equipment only as a last resort, not a first line of defence
- Review the effectiveness of controls regularly
- Provide information and training so workers understand the risks and know how to protect themselves
- Ensure control measures don’t create new risks elsewhere
The Hierarchy of Controls
COSHH follows a hierarchy when it comes to managing risk, arranged from most effective to least effective. The goal is always to start at the top and only move down the list when the options above aren’t practicable.
Elimination means removing the hazardous substance entirely. If a process doesn’t actually need a toxic solvent, stop using it. Substitution means replacing a dangerous substance with a less harmful one, like switching to a water-based cleaner instead of a chemical one. Engineering controls physically separate workers from the hazard through ventilation systems, enclosed processes, or extraction equipment. Administrative controls change how people work: limiting time spent in exposure zones, rotating tasks, or establishing safe procedures. Personal protective equipment (gloves, masks, respirators) sits at the bottom because it depends on being worn correctly every time and protects only the individual wearing it.
Workplace Exposure Limits
The UK sets legal limits on how much of a substance workers can be exposed to over a working day or a shorter reference period. These limits are published in a document called EH40, maintained by the HSE. It lists hundreds of substances alongside their maximum allowable airborne concentrations. Employers are required to keep exposure below these limits, and COSHH risk assessments should reference them when relevant. If monitoring shows exposure approaching or exceeding a limit, the employer must take immediate action to reduce it.
When Health Surveillance Is Required
In some cases, COSHH requires employers to provide ongoing health checks for exposed workers. Health surveillance becomes a legal duty when three conditions overlap: there is a known disease linked to the substance being used (such as occupational asthma, dermatitis, or certain cancers), it is possible to detect the disease or early warning signs through medical checks, and workplace conditions make it likely that the disease could develop.
Health surveillance might involve regular skin checks for workers handling sensitising chemicals, lung function tests for those exposed to respiratory hazards, or blood or urine tests depending on the substance. The purpose is to catch problems early, before they become serious or irreversible. Records of health surveillance must be kept for at least 40 years.
What Employees Are Expected to Do
COSHH isn’t only about employer obligations. Workers have a responsibility to use the control measures and protective equipment provided to them, follow safe working procedures, and report any problems with equipment or exposure controls. If you notice a ventilation system isn’t working or your gloves are degrading, you’re expected to raise it. You also have the right to refuse work you believe poses a serious and immediate danger to your health, provided the concern is genuine.
Training is a two-way street under COSHH. Your employer must explain the risks you face and how to use controls properly, delivered in a language and vocabulary you can understand. But you’re expected to actually follow that training in practice.
Who Needs to Know About COSHH
COSHH applies to virtually every workplace in the UK where hazardous substances are used, produced, or encountered. That includes obvious settings like factories, laboratories, and construction sites, but also hairdressers (hair dye chemicals), bakeries (flour dust), offices (printer toner, cleaning products), farms (pesticides, animal pathogens), and healthcare facilities (disinfectants, biological agents). If you work somewhere that uses any substance capable of causing harm through inhalation, skin contact, or ingestion, COSHH applies to your employer.