Isocyanates are highly reactive chemicals used in the manufacture of polyurethane products, e.g. flexible and rigid foam, fibre, coatings, paints, lacquers and varnishes, expanding foam and glues.

They are used extensively in the automotive industry, auto body repair, and as products used in construction and building materials.

Paints containing isocyanate are commonly referred to as 2-pack or "2K" isocyanate-containing paints; some water-based paints also contain isocyanates.

Isocyanates come in different chemical forms, the most commonly used are methylene diphenyl diisocyanate (MDI), toluene diisocyanate (TDI), and hexamethylene diisocyanate (HDI); TDI is more hazardous because it is more volatile and the vapour can be breathed in.

You must check the information on the packaging and safety data sheet, supplied by the manufacturer to find out what the product contains.

Isocyanates are extremely irritant and are respiratory sensitisers; exposure can lead to skin irritation, dermatitis and lung diseases such as occupational asthma.

Health Effects

Respiratory sensitisation

Breathing in isocyanates can cause you to develop an allergic reaction (respiratory sensitisation). Sensitisation may develop as a result of a large single exposure, or from repeated exposure at lower levels.

Once you’ve become sensitised, it can trigger asthma symptoms when you breathe it in (occupational asthma). You may have been at your place of work for weeks, months or even years before you start having asthma symptoms.

Symptoms can develop immediately after breathing in isocyanate vapour or mists but can also appear several hours later outside working hours in the evening or early morning.

People who already have asthma are more prone to sensitisation and other adverse reactions; in some cases, death has occurred from a severe asthma attack after isocyanate exposure.

Early signs of respiratory sensitisation to isocyanates include one or more of the following:

  • chest tightness
  • persistent cough
  • wheezing
  • breathlessness
  • flu-like shivers
  • recurring blocked or runny nose
  • recurring sore or watering eyes

Skin exposure

Isocyanates are skin irritants and cause inflammation and dermatitis; there is some evidence that skin exposure can also cause respiratory sensitisation.

Eye exposure

Isocyanates are irritant to the eyes and splashes can cause severe conjunctivitis.

Main Uses of Isocyanates

The major health risk for isocyanate is from breathing in mists, aerosols or vapour.

These are generated from activities such as

  • spraying of isocyanate containing paints
  • pouring of isocyanate containing binders to make moulds and resins
  • use of isocyanate containing primers, adhesives, resins
  • manufacture of polyurethane rubber, foam and plastics


You must prevent exposure to isocyanate or where this is not possible control it to as low as reasonably practical.

You must;

  • identify and assess who is at risk, including others who may be affected by the work.  
  • implement appropriate and effective control measures to eliminate the use of isocyanates or reduce exposure
  •  carry out health surveillance and monitoring, including biological monitoring to assess whether controls are adequate and are being used properly

Where possible eliminate or reduce isocyanate risks;

  • use products that do not contain isocyanates or contain a less volatile form
  • avoid unnecessary spraying as this creates airborne mists and droplets,
  • use a brush or roller.

Where spraying cannot be avoided;

  • spray in a booth or enclosed area fitted with local exhaust ventilation (LEV).
  • choose spray equipment that reduces the amount of airborne spray, e.g. high-volume low-pressure (HVLP) spray guns or airless spraying.
  • use constant flow air-fed breathing apparatus (BA) for spraying.
  • keep all non-essential people away from the work area, particularly anyone who is already sensitised to isocyanates and take into account any spray drift.
  • make sure the work area is ventilated, e.g. open doors and windows or use mechanical ventilation.

Use respiratory protective equipment (RPE);

  • for tasks which create an aerosol, e.g. brushing or rollering, particularly in enclosed spaces,
  • or if using products with significant amounts of TDI.
  • wearers must be face fitted and it is particularly important to select the correct vapour filter, e.g, P3 particulate filters provide protection against spray mist but do not protect you from vapours; you will need a gas/vapour filter for these.
  • wear appropriate personal protective equipment, disposable types are preferable to prevent contact with contaminated clothing.
  • eye protection (e.g. goggles or a face shield) should be worn during work where there is a risk of splash or aerosol generation.
  • protective gloves or gauntlets, should be worn to prevent skin exposure; make sure they are suitable for the products being used and the breakthrough time and permeation rate are right for the type and length of the work.

Maintain good hygiene practice;

  • wash off any product on the skin as soon as possible.
  • clean and wash exposed skin at break times and after finishing work.
  • use a skin care product to replace the natural oils that help keep the skin’s protective barrier working properly.

Guidance on risk assessment, working with and preventing exposure to isocyanates are contained in a range of HSE publications, listed below.


Guidance on working with isocyanates and controlling the risks is available at the following links:

Key Legislation