Occupational Asthma (OA) is a type of asthma caused by inhaling hazardous substances or irritants at work. It is important to distinguish between occupational asthma and aggravation of pre-existing asthma, as management and compensation can differ. There are two main forms of OA first described is sensitizer-induced OA caused by IgE-mediated or other immune responses to specific workplace agents i.e. high molecular weight sensitizers (animal proteins, flour, or natural rubber latex) and low-molecular-weight chemicals such as (diisocyanates, colophony). This type of OA develops after a latency period between the first exposure and the onset of symptoms. Secondly, is irritant-induced OA including reactive airway dysfunction syndrome which is caused by non-immunological stimuli which occur after accidental exposure to a very high concentration of a workplace irritant. Once a person has been sensitized to one of the materials, exposure in low quantities will exacerbate asthma1.
Figure 1 : Natural history of the development of sensitization and OA.
Steps are in boxes above the horizontal line, whereas modulating factors are listed below2
Occupational Asthma and the workplace
According to the Health and Safety Executive (HSE) Health Surveillance ‘is a risk-based scheme of repeated health checks for the early identification of ill-health caused by work.’ In their latest documents on OA – ‘Health Surveillance for occupational asthma’ they list the main causes of occupational asthma are; Isocyanates (e.g. two-pack spray paints), flour dust, grain dust, wood dust, latex, rosin-based solder flux fume, laboratory animals, cleaning products, enzymes, stainless-steel welding, aldehydes, glues, and resins3.
They also list a group of high-risk occupational groups which include bakeries, food manufacturing, beauty industry, cleaning services, healthcare workers, spray painters, repairers (including electronics), welders, woodworkers (including forestry), workers exposed to metal working fluids, seafood processing, laboratory work, and detergent manufacturing3.
Figure 2 : HSE recommendations for when health surveillance should be considered in workers3
What are the signs and symptoms?
People who get OA may have been healthy before and never had asthma or they may have had asthma as a child, and it returned. If the worker already has asthma, it may be worsened by being exposed to certain substances at work. Workers might be in a workplace for a while before symptoms are noticed because it takes a while for your immune system to become sensitive to workplace triggers. Once sensitization takes place it can trigger asthma symptoms the next time the worker encounters the trigger even in small amounts. Common symptoms are highlighted in figure 3. However, it is important to note people with a family history of allergies are more likely to develop occupational asthma, particularly to some substances such as flour, animals, and latex. But even if you don’t have a history, you can still develop this disease if you’re exposed to conditions to induce it. Also, if you smoke, you’re at a greater risk of developing asthma. If symptoms are detected early and exposure has been modified the risk of developing long-term asthma is reduced.
Figure 3 : HSE list of common symptoms associated with OA3
Initial diagnosis of OA involves a consultation with a doctor, to go over the prevalence of symptoms when they occur, type of work, and medical history, example questions are highlighted in table 3.
Figure 4 : Example questionnaire investigation OA4
However, a diagnosis of occupational asthma should not be made based on a positive history alone, diagnostic tests performed in secondary care are highly valuable in aiding the diagnosis, the tests include:
Spirometry test – This is a lung function test where a person will need to take a deep breath and blow air out into the spirometer forcibly. Spirometry is measuring the breathing capacity and airways cross-sectional areas of the lungs. It is particularly useful in determining the presence or absence of obstructive lung disease among workers. Tests should include the 1- second forced expiratory volume FEV1, the forced vital capacity FVC and the ratio of these two measurements. Quality spirometers must be used for annual spirometry testing because charting the annual decline of lung function over the employment period will be impossible without accurate measurements. A decline of 30mL per year is normal; over 100mL a year is abnormal. As these levels of change are relatively small, it is essential that the spirometers used for testing are not just highly accurate but are consistently so over time. Those performing spirometry testing need to be confident that the test results and year-on-year comparisons can be relied upon.
Fractional exhaled nitric oxide (FeNO) test—The FeNO test measures the amount of nitric oxide present in the breath, which can determine the presence of inflammation in the airways, which might indicate asthma5.
Allergy test or Skin prick test – This test involves using various allergens to assess whether the worker has a reaction to the allergens used which could be linked to their occupational asthma, however, if symptoms are caused by irritants instead of allergens there will be no visible reaction on the test5.
Challenge test – This test involves the worker inhaling the known or thought to be causing the symptoms, to see if any trigger asthma symptoms. This is quite a difficult test and is performed in specialist centers where the worker can be closely monitored5.
How can it be prevented?
If OA is detected early sometimes symptoms can be stopped, as long as the OA is diagnosed quickly, the cause is identified and exposure to the trigger is stopped. When symptoms will stop will vary, for some workers, it may be straight and for others take longer.
Even if symptoms do go away, the substance that set them off will always be a trigger for the worker, so they will need to avoid it, this may mean avoiding similar workplaces. The best way to prevent occupational asthma is to control exposure to chemicals and other substances that the workers may be sensitive to or that are irritating. Workplaces can implement better control methods to prevent exposures, use less harmful substances and provide personal protective equipment (PPE) for workers6. Medications may help relieve symptoms and control inflammation associated with occupational asthma. As well as changes of lifestyle factors contributing to the OA can be made for example if the worker smokes they should quit as being smoke-free may help prevent or lessen symptoms of OA or if the worker is obese, losing weight can help improve symptoms and lung function. Employers must also make the effort to keep workers safe and provide the workers with relevant material such as a safety data sheet for each hazardous chemical used in the workplace and share this information with the workers.
- Occupational asthma: an approach to diagnosis and management Susan M. Tarlo, Gary M. Liss CMAJ Apr 2003, 168 (7) 867-871;
- Malo, J. and Chan-Yeung, M., 2001. Occupational asthma. Journal of Allergy and Clinical Immunology, 108(3), pp.317-328.
- Asthma + Lung UK. 2022. Occupational asthma and work aggravated asthma | Asthma UK. [online] Available at: <https://www.asthma.org.uk/advice/understanding-asthma/types/occupational-asthma.> [Accessed 27 September 2022].
- Nicholson, P., Cullinan, P. and Burge, S., 2012. Concise guidance: diagnosis, management and prevention of occupational asthma. Clinical Medicine, 12(2), pp.156-159.
- Mayo Clinic. 2022. Occupational asthma – Symptoms and causes. [online] Available at: <https://www.mayoclinic.org/diseases-conditions/occupational-asthma/symptoms-causes/syc-20375772> [Accessed 27 September 2022].