occupational asthma
3 min read
Updated 2026-03-23
Contents
occupational asthma
Two distinct entities: sensitiser-induced (true occupational asthma — new disease caused by work) vs work-exacerbated (pre-existing asthma worsened by workplace irritants). The distinction has major implications for prognosis, management, and medicolegal outcome. Early removal from exposure is the most important intervention for sensitiser-induced disease.
classification
| Sensitiser-induced OA | Irritant-induced OA (RADS) | Work-exacerbated asthma | |
|---|---|---|---|
| Mechanism | Immunological sensitisation (latency period) | High-level irritant exposure → airway injury | Pre-existing asthma worsened by workplace triggers |
| Latency | Weeks to years of exposure before symptom onset | Onset within 24h of single high-dose exposure | N/A |
| Pre-existing asthma | No (new disease) | No | Yes |
| Prognosis with removal | May improve or resolve | Often persistent | Improves but underlying asthma remains |
| Medicolegal | Compensable workplace disease | Compensable | Generally not compensable as occupational disease |
common sensitisers
| Agent | Occupation |
|---|---|
| Isocyanates (TDI, MDI, HDI) | Spray painters, insulation workers, auto body |
| Flour / grain dust | Bakers, millers |
| Wood dust (western red cedar) | Carpenters, sawmill workers |
| Latex | Healthcare workers |
| Laboratory animals | Research technicians |
| Enzymes (subtilisins) | Detergent manufacturing |
| Metals (platinum salts, chromium) | Welders, platers |
| Persulfates | Hairdressers |
isocyanates
The most common cause of occupational asthma in industrialised countries. Exposure can occur even at very low concentrations. Ask about spray painting, foam manufacturing, and insulation work.
when to suspect
- Asthma onset as an adult with no prior history (especially if atopic) — 5–20% of new adult-onset asthma is attributable to occupational exposure
- Occupational rhinitis preceding asthma symptoms (may precede OA by up to a year — an early warning sign)
- Symptoms improve on weekends, holidays, or time away from work
- Symptoms worsen during or shortly after work shifts
- Multiple co-workers with similar symptoms
- Exposure to known high-risk agents
diagnosis
Step 1: Confirm asthma — objective evidence of variable airflow limitation (spirometry, methacholine challenge)
Step 2: Establish work-relatedness
| Test | Method | Notes |
|---|---|---|
| Serial PEF monitoring | ≥ 4 readings/day for ≥ 2 weeks at work and 2 weeks away | Gold standard for demonstrating work-related variability; interpret with OASYS score; requires patient compliance |
| Methacholine challenge | At work vs after ≥ 2 weeks away | PC20 decreases (worsens) at work; ≥ 3.2-fold improvement in PC20 off work supports OA |
| Specific IgE / skin prick | For high-molecular-weight agents (proteins, latex) | Supports sensitisation; does not confirm causation |
| Specific inhalation challenge (SIC) | Controlled exposure in specialised lab | Gold standard for confirming specific agent; limited availability |
Step 3: Identify the causative agent — occupational hygiene assessment, MSDS review
management
sensitiser-induced OA
- Complete removal from exposure — the earlier the better. Continued exposure leads to progressive, irreversible decline
- Pharmacological treatment same as general asthma guidelines
- Workers’ compensation referral — document diagnosis thoroughly
- Monitor after removal: improvement may take months to years; up to 70% have persistent asthma despite removal — prognosis improves with earlier diagnosis and removal
- Retraining / job modification if same workplace
work-exacerbated asthma
- Optimise asthma treatment per asthma guidelines
- Reduce workplace irritant exposure (engineering controls, PPE)
- Complete removal from work usually not necessary
- May benefit from pre-shift bronchodilator use in some cases
what NOT to do
- Label all work-related symptoms as “occupational asthma” — work-exacerbated asthma is far more common and managed differently
- Diagnose OA without objective evidence (serial PEF, methacholine, or SIC)
- Delay removal from exposure in confirmed sensitiser-induced OA — prognosis worsens with continued exposure
- Forget to notify public health/workplace safety where mandated
- Assume normal spirometry excludes OA — spirometry may be normal between exposures; methacholine challenge or serial PEF is needed