Occupational Asthma and Work-Related Lung Disease
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Direct answer
Occupational asthma is asthma caused or worsened by specific workplace agents, classed as sensitiser-induced or irritant-induced. Sensitiser asthma is immunological and has a latency period of months to years, while irritant-induced asthma follows a single high-level exposure. Serial peak flow recorded at work and away from work links symptoms to the workplace. Removing the exposure is the most effective step, and early diagnosis prevents permanent damage.
What you must remember
- Sensitiser asthma: immunological and often IgE-mediated, with a latency period of months to years; agents include flour, isocyanates, wood dust and latex.
- Irritant asthma: reactive airways dysfunction syndrome develops within 24 hours of a high-level exposure, such as chlorine, ammonia or smoke, and symptoms can persist for months.
- Byssinosis: chest tightness on the first shift after a break, from cotton, flax or hemp dust in textile work, and repeated exposure causes chronic bronchitis.
- Baker's asthma: a classic sensitiser asthma from flour dust, with enzymes such as alpha-amylase implicated, often accompanied by rhinitis.
- Serial peak flow: recorded several times daily at work and away from work, where a fall at work with recovery away supports the diagnosis.
- Specific inhalation challenge: the reference standard for proving the link, performed only in specialist centres.
A baker with a Monday-to-Friday cough
A 34-year-old baker has two years of chest tightness and a cough that worsens during the working week and eases at weekends. He has rhinitis, and his peak flow falls during each shift and recovers on his days off.
Occupational asthma is classified by mechanism, and the classification decides both the investigation and the advice. The table compares the two main forms.
| Feature | Sensitiser asthma | Irritant asthma (RADS) |
|---|---|---|
| Mechanism | Immune, often IgE-mediated | Direct airway injury |
| Latency | Months to years | Within 24 hours |
| Exposure | Repeated, lower level | Single, high level |
| Course after leaving work | Often improves, with time | Can persist for months |
| Common agents | Flour, isocyanates, latex | Chlorine, ammonia, smoke |
The workplace history, especially the time from exposure to symptoms, usually separates the two forms. Serial peak flow confirms the link when the history is uncertain, and it is recorded before, during and after the working day. Exposure removal is considered early, because the outcome depends on how soon the worker leaves the trigger.
Where the exam tests the workplace link
The exam tests whether you prove the link and whether you advise the right exposure control.
- Trap: diagnosing occupational asthma from history alone Correct: serial peak flow records or specific inhalation challenge are needed to confirm the link.
- Trap: advising continued exposure because inhaled steroids control the symptoms Correct: medicines do not stop progression in sensitiser asthma, so removing the exposure is essential.
- Trap: calling byssinosis a purely acute condition Correct: repeated exposure causes chronic bronchitis and a permanent fall in lung function.
- Trap: dismissing flour-related wheeze as ordinary allergy Correct: baker's asthma is a classic sensitiser occupational asthma and needs exposure review.
Frequently asked questions
What is the difference between sensitiser and irritant occupational asthma?
Sensitiser occupational asthma is immunological and has a latency period of months to years, whereas irritant occupational asthma follows a single high-level exposure. Reactive airways dysfunction syndrome is the typical irritant form and begins within 24 hours of exposure.
Which investigation proves occupational asthma?
Serial peak flow recorded at work and away from work is used to support occupational asthma, and specific inhalation challenge is the reference standard for proving the link. Specific inhalation challenge is performed only in specialist centres because it can provoke severe attacks.
Why is byssinosis associated with Monday chest tightness?
Byssinosis causes chest tightness on the first shift after a break, such as Monday morning after a weekend away from cotton dust. Repeated exposure leads to chronic bronchitis and a permanent fall in lung function, so exposure control is the key intervention.
Why is baker's asthma important in exams?
Baker's asthma is a classic sensitiser occupational asthma caused by flour dust, with enzymes such as alpha-amylase implicated. It is often accompanied by rhinitis, and removal from flour exposure is the key step in management.