Occupational asthma: how work exposure causes it

Through sensitisation - repeatedly breathing a respiratory sensitiser at work makes the immune system and airways hypersensitive to that substance, so once sensitised, exposure triggers asthma; it's not direct damage but the person's own immune reaction to the substance causing their asthma. Work exposure causes occupational asthma mainly through sensitisation. When a susceptible person repeatedly breathes a respiratory sensitiser at work - isocyanates, flour dust, wood dust, solder flux and the other causes - their immune system can become sensitised to that substance, primed to react to it. Once this has happened, the person is sensitised, and their airways are hypersensitive to the substance. From then on, exposure triggers an asthmatic response (wheezing, chest tightness, breathlessness). So the harm isn't direct chemical damage from the substance; it's the immune system being turned hypersensitive, so the person's own reaction to the substance causes their asthma. This is what 'sensitiser' means - a substance that makes you hypersensitive to it. Several features follow: it usually develops after a symptom-free latency (weeks, months or years of exposure); once sensitised, the person reacts to even tiny amounts; reactions can be delayed (appearing hours after exposure, away from work); and it's usually permanent (no cure). So work exposure causes it by sensitising the airways over time, which is why preventing the exposure matters so much. So by sensitising the airways so exposure then triggers asthma. So through sensitisation to a workplace substance. This is general information, not clinical advice. This is general information.

It's the symptom-free period of exposure during which a person is being sensitised but hasn't yet developed asthma - so occupational asthma appears only after weeks, months or years of exposure, not immediately; the worker feels fine and doesn't know they're being sensitised, so the exposure often continues uncontrolled. The latency period in occupational asthma is the symptom-free stretch of exposure during which a person is being sensitised to a substance but hasn't yet developed asthma. Sensitisation isn't instant - it develops over a period of repeated exposure, and during that period (which can be weeks, months or years) the person is becoming sensitised without any symptoms. So occupational asthma typically doesn't appear on the first day or even the first months; it appears after this latency, once sensitisation has developed. The latency matters for two reasons. First, the worker feels fine throughout it and has no idea they're being sensitised - the process is silent, so there's no warning that harm is developing, and the exposure often continues uncontrolled until the asthma appears. Second, it breaks the obvious link between the substance and the disease - the asthma appears long after the exposure began, so it's not obviously connected to the workplace substance, which can delay recognition. So the latency is why occupational asthma develops silently before it declares itself, and part of why it's so easily missed and left uncontrolled. So it's the silent period of sensitisation before the asthma appears. So the symptom-free time while sensitisation builds. This is general information, not clinical advice. This is general information.

Because sensitisation makes the airways hypersensitive to the substance, so once sensitised the person reacts to far less than it took to sensitise them - exposures tolerated during the latency now trigger asthma; this means a sensitised worker can't safely be exposed at all, even at low levels. A sensitised person reacts to even small amounts of the substance because sensitisation has made their airways hypersensitive to it. During the latency (before sensitisation), the person could breathe the substance without an asthmatic reaction - they were tolerating it while being sensitised. But once sensitisation has developed, their immune system and airways are primed to over-react to the substance, so they now react to it - and to far less of it than it took to sensitise them in the first place. So exposures that would have been tolerated before now trigger asthma. This means a sensitised worker can't safely be exposed to the substance at all, even at low levels or briefly - the slightest exposure can set off their asthma. It's a grim consequence, because it means that once someone is sensitised, simply reducing their exposure isn't enough; they generally need to avoid the substance entirely, which usually means they can't keep doing that work. It's also why controlling exposure to a low level protects people from becoming sensitised, but doesn't help someone who already is. So they react to tiny amounts because sensitisation has made them hypersensitive. So because sensitisation makes the airways exquisitely reactive. This is general information, not clinical advice. This is general information.

Usually not - the sensitisation is generally permanent, so once occupational asthma has developed it doesn't reverse; the sensitised worker reacts to the substance for life and typically can't keep working with it, so preventing the exposure before sensitisation is the only real protection, and early removal from exposure limits the harm. Usually not - occupational asthma from a sensitiser generally can't be cured, because the sensitisation is usually permanent. Once a person's airways have become sensitised to the substance, that hypersensitivity generally doesn't reverse - so the occupational asthma, once developed, is a lasting condition. This means a sensitised worker reacts to the substance for life (and to even small amounts), and typically can't keep working with it, because continued exposure triggers and worsens their asthma - often a career-ending outcome. Because it can't be cured, the emphasis has to be entirely on prevention: controlling the exposure before anyone is sensitised, so the asthma never develops. There's no fixing it after the fact. That said, catching occupational asthma early - recognising it and removing the person from exposure promptly once it appears - matters, because continued exposure after sensitisation tends to make the asthma worse and more established, whereas early removal can limit the harm (even if it doesn't cure it). So the priorities are preventing the exposure (before sensitisation) and, failing that, early detection and removal. So usually no - it's permanent, so prevention is what counts. So usually not; prevent it rather than cure it. This is general information, not clinical advice. This is general information.

Because the asthmatic reaction to a sensitiser can be delayed - appearing hours after exposure, in the evening or at night - so a worker exposed by day can react at home; this can hide the work link, though a pattern of symptoms worse on work days or improving on days off is a clue. Occupational asthma symptoms can appear away from work because the asthmatic reaction to a sensitiser can be delayed, not just immediate. While some reactions come on soon after exposure, others appear hours later - in the evening or at night, away from work. So a worker exposed to the sensitiser during their shift might have an asthmatic reaction that evening at home, rather than at work. This delayed pattern can obscure the link to work: the worker feels ill at home, hours after their shift, and may not connect it to the workplace substance - it can feel like ordinary asthma appearing out of nowhere. This makes occupational asthma easy to miss, both for the worker and sometimes their doctor. However, there are clues to the occupational cause: a pattern of symptoms that are worse on work days, or that improve on days off, weekends and holidays (when the person is away from the exposure), points to a work-related cause. Recognising this pattern helps identify occupational asthma despite the delayed, away-from-work symptoms. This is also why health surveillance (which looks for such patterns) is valuable. So symptoms appear away from work because the reaction can be delayed by hours. So because the reaction can be delayed, striking at home. This is general information, not clinical advice. This is general information.

Because it develops silently (through a latency) and can't be cured, so by the time it appears the person is permanently sensitised - there's no fixing it after the fact; the only real protection is controlling the exposure (with LEV and the hierarchy) before sensitisation, so workers don't breathe enough to become sensitised. Preventing exposure is the key to occupational asthma because of how the disease works: it develops silently and can't be cured, so you can't rely on catching and fixing it. The latency means it develops unseen (the worker is sensitised over a period with no symptoms); the permanence means that once it appears, it can't be undone (the sensitisation doesn't reverse); and the tiny trigger means that once sensitised, the person can't be exposed at all. So by the time occupational asthma appears, the person is already permanently sensitised - there's no fixing it after the fact. This leaves only one real protection: preventing the exposure that causes sensitisation in the first place, so workers don't breathe enough of the sensitiser to become sensitised. That means controlling the substance - reducing it, capturing it at source with local exhaust ventilation (LEV) so it isn't breathed, and using RPE where needed - keeping exposure as low as reasonably practicable (since for a sensitiser there's no safe level). The LEV must be kept working and tested to keep the exposure controlled. Health surveillance can catch early sensitisation as a backstop, but prevention through exposure control is the real defence. So because the asthma can't be caught and cured, preventing the exposure is the only protection. So because it develops unseen and can't be cured. This is general information, not clinical advice. This is general information.