Work-related asthma includes both occupational asthma and work-exacerbated asthma. Occupational asthma is new-onset asthma that is caused by exposure to either allergens or irritants in the workplace and is further classified as either sensitizer-induced or irritant-induced. Work-exacerbated asthma is pre-existing asthma that is worsened by workplace conditions, such as temperature extremes, dust, cleaning products, damp environments or environmental allergens. Symptoms of work-related asthma include dyspnea, wheezing, cough, and, occasionally, upper respiratory allergy symptoms. Diagnosis is based primarily on occupational history, including assessment of job activities, exposures in the work environment, and a temporal association between work and symptoms. Treatment involves exposure reduction (and if necessary removal), asthma medications as needed, and close monitoring.
(See also Overview of Environmental and Occupational Pulmonary Disease and Asthma.)
Approximately 15% of adult-onset asthma is attributed to occupational exposure (1, 2). Work-related asthma should be suspected in all adults with asthma, especially those with new-onset or worsening asthma.
Workplaces commonly contain multiple irritants and allergens that can cause or exacerbate asthma. Often identifying the specific agent (eg, cleaning product, hair care product) is challenging and usually unnecessary. However, it is important to distinguish work-related asthma from other airway disorders that are related to the workplace, such as upper airway irritation, vocal cord dysfunction, hypersensitivity pneumonitis, and chronic bronchitis.
Workplace-related asthma can continue to cause symptoms even after exposure to the inciting irritant or allergen has ceased.
Sensitizer-induced occupational asthma
Immune-mediated mechanisms involve both IgE- and non–IgE-mediated hypersensitivity reactions to workplace triggers. Risk of developing sensitizer-induced asthma varies by occupation and the specific agents used at the workplace. Further, dose of exposure is a factor in initial sensitization, and atopy is also an important risk factor for high molecular weight antigens (3).
Irritant exposure and reactive airways dysfunction syndrome (RADS)
Irritant-induced asthma refers to asthma that occurs following exposure to respiratory irritants at work. The pathogenesis of irritant-induced asthma is due to cell damage and inflammation, in contrast to the immune-mediated mechanisms of sensitizer-induced asthma. A high level of exposure to an irritant, such as in a workplace accident or chemical spill, can result in reactive airways dysfunction syndrome (RADS).
RADS refers to the new onset of asthma symptoms within 24 hours of a high-level exposure to a known irritant. Additional RADS criteria include pulmonary function testing consistent with airway hyperresponsiveness, persistence of symptoms for ≥ 3 months, and lack of pre-existing asthma or other lung disease to explain symptoms.
In addition to RADS, irritant-induced asthma also includes development of asthma in workers with chronic exposure to moderate levels of irritants. A growing body of case reports and case series describes onset of asthma following chronic low-level exposure to irritants, such as cleaning products and disinfectants (4).
Work-exacerbated asthma
Work-exacerbated asthma is asthma that is not caused by irritants specific to the workplace but is pre-existing asthma that is worsened by asthma triggers at work. Work exposures that can exacerbate asthma include temperature extremes, humidity and damp environments, dust, and cleaning products. Patients may also be exposed to common environmental allergens at work that have the potential to exacerbate asthma. Temporal pattern of the symptoms of work-exacerbated asthma depend on the pattern of exposure and can be transient, in the case of unique exposures such as remodeling work, or daily, in cases where the exposure occurs during regular job duties (5).
General references
1. Blanc PD, Annesi-Maesano I, Balmes JR, et al: The Occupational Burden of Nonmalignant Respiratory Diseases. An Official American Thoracic Society and European Respiratory Society Statement. Am J Respir Crit Care Med 2019;199(11):1312-1334. doi: 10.1164/rccm.201904-0717ST
2. Hoy R, Burdon J, Chen L, et al. Work-related asthma: A position paper from the Thoracic Society of Australia and New Zealand and the National Asthma Council Australia. Respirology 2020; 25(11):1183-1192. doi:10.1111/resp.13951
3. Laditka JN, Laditka SB, Arif AA, Hoyle JN. Work-related asthma in the USA: nationally representative estimates with extended follow-up. Occup Environ Med 2020; 77(9):617-622. doi:10.1136/oemed-2019-106121
4. Lemiere C, Lavoie G, Doyen V, Vandenplas O. Irritant-Induced Asthma. J Allergy Clin Immunol Pract 2020; 10(11):2799-2806. doi:https://dx.doi.org/10.1016/j.jaip.2022.06.045
5. Maestrelli P, Henneberger PK, Tarlo S, et al. Causes and Phenotypes of Work-Related Asthma. Int J Environ Res Public Health 2020; 17(13):4713. doi:https://dx.doi.org/10.3390/ijerph17134713
Symptoms and Signs of Work-Related Asthma
Symptoms of work-related asthma caused by sensitization to an agent in the workplace typically develop over a latency of weeks to years. Once sensitized, the worker can respond to very low concentrations of the agent, making exposure control challenging for sensitized workers.
Typical symptoms include shortness of breath, chest tightness, wheezing, and cough, temporally related to work. Rhinitis and conjunctival symptoms are more common with high molecular weight allergens and may precede the typical symptoms of asthma by months or years.
Symptoms typically develop and/or worsen at work after exposure to the sensitizing agent and improve when the patient is away from work (eg, on weekends and holidays). Late asthmatic responses, symptoms starting 4 to 6 or more hours after exposure, are common with low molecular weight agents and can make the association with work challenging to recognize. Continued exposure at work causes the symptoms to become more chronic and persistent, and the association with work can become less apparent.
Diagnosis of Work-Related Asthma
Clarify the diagnosis of asthma (including pulmonary function testing)
Identify work exposures that are associated with asthma
Clarify the temporal relationships between asthma and work
Work-related asthma should be considered in all adults with new-onset or worsening asthma. Improvement in asthma symptoms when the patient is away from work (eg, on weekends or holidays) should raise suspicion of work-related asthma. Worsening symptoms or greater use of asthma medications related to work should also prompt further investigation. As the diagnosis of work-related asthma can impact employment, it is important to document the diagnosis of asthma, known or suspected causative agents, and the rationale for work-relatedness.
Clinicians should note typical symptoms of asthma and clinical improvement in response to inhaled bronchodilators and corticosteroids.
Spirometry may be helpful in establishing a diagnosis of asthma if it shows variable airflow obstruction, which is most commonly demonstrated by improvement in forced expiratory volume in 1 second (FEV1) after taking an inhaled bronchodilator. Improvement in spirometry results after asthma treatment or after removal from triggering exposures and elevation in exhaled nitric oxide also support a diagnosis of asthma.
Asthma is characterized by variable airflow obstruction, so many patients with asthma have normal spirometry results when they are not symptomatic or when they are being treated. Normal spirometry and a lack of response to inhaled bronchodilators do not rule out the diagnosis of asthma, especially when the patient is taking asthma medication or is not symptomatic.
A patient with work-related respiratory symptoms in whom asthma is not documented may have another work-related condition such as vocal cord dysfunction, upper respiratory tract irritation, hypersensitivity pneumonitis, chronic obstructive pulmonary disease (COPD), or chronic bronchitis. Testing may be needed to rule out alternate diagnoses.
Following clarification of the asthma diagnosis, the clinician should document the timing, onset, and progression of asthma in relationship to work and also non-workplace exposures to asthma triggers. A thorough occupational history, including job title, industry, job tasks, and description of the work environment and materials used should be obtained. Asthma becomes more generalized over time, thus in trying to identify the causative factor(s), in addition to evaluating the patient's current symptoms, the clinician should focus on when the patient’s asthma began and/or worsened, especially if the patient is no longer at the workplace in question.
Safety data sheets, mandatory at all work sites in the United States, can be used to identify irritants and allergens that can cause asthma. However, the absence of a known irritant on the safety data sheet does not exclude the diagnosis of work-related asthma. For the few asthma-causing agents for which commercially available allergy testing is available, such as for certain animals and grains, allergy testing can help identify a causative agent, although false negatives and positives are possible.
Once work and non-work exposures have been characterized, it is important to assess and document the relationship of the patient’s symptoms to work. Serial peak flow measurements taken while the patient is at and also while away from work, changes in inhaler use at and away from work, and allergy testing can provide greater diagnostic certainty. It is more challenging to diagnose work-related asthma once the patient is away from the causative workplace. Thus, unless the patient is having severe symptoms, it is generally preferable not to remove a patient from work while evaluating a possible diagnosis of work-related asthma.
Work-exacerbated asthma
The diagnosis of work-exacerbated asthma is based on history of pre-existing asthma (symptoms, medical history, medication usage, variable airflow obstruction) and the presence of conditions at work that can exacerbate asthma, which includes common irritants, allergens, extremes of temperature and humidity, and physical exertion in conjunction with increase in asthma symptoms and/or inhaler use. Worsening asthma related to work can be documented by noting worsening symptoms, increased frequency of physician visits for asthma symptoms, increased use of asthma medications, or rarely, worsening lung function (peak flows, spirometry) related to work. Recurrence of asthma that had resolved may be new-onset work-related asthma.
Treatment of Work-Related Asthma
Eliminating exposure
Pharmacologic treatment for asthma
Workplace modification or change
The pharmacologic treatment of work-related asthma is similar to that of other types of asthma. For all types of work-related asthma, triggering exposures and conditions in the workplace and at home should be minimized. Patients should be monitored for worsening asthma symptoms and increasing medication use.
With sensitizer-induced occupational asthma, once sensitized, patients can react to extremely low levels of airborne exposure. Thus, the recommended management consists of identification of and complete removal from further exposure to the sensitizing agent. Given that complete removal from the workplace can involve substantial socioeconomic consequences, transfer to a different work area at the same workplace or improving engineering controls is sometimes tried. In situations with potential for ongoing exposure to the sensitizer, close monitoring for worsening asthma is essential, including symptoms, medication usage and lung function. Early recognition and prompt removal from the sensitizing agent result in better outcomes, but asthma commonly persists away from the sensitizing agent.
For patients with irritant-induced occupational asthma and work-exacerbated asthma, the hope is that workers can continue their current jobs if adequate measures are implemented to reduce triggering exposures and conditions. These include better engineering controls of irritant exposures and accommodations to avoid certain job tasks or locations, such as work in a hot or cold room. Regular monitoring of asthma symptoms and control is important. If the patient’s asthma worsens at work, further work modifications, including change in employment, may be necessary. Standard asthma treatment, including pharmacologic treatment and minimizing home and environmental triggers, is recommended.
Both sensitizer-induced and irritant-induced asthma commonly persists even when patients are away from the causative exposure, and patients may require long-term use of asthma medications. Clinicians should document the diagnosis of work-related asthma and specific causative factors before making recommendations about work.
Prevention of Work-Related Asthma
Timely recognition of work-related asthma plays a key role in its further prevention. When a case of occupational asthma is identified in the workplace, the clinician should consider the potential for other workers to be exposed. Communication with the workplace and public health officials facilitates further evaluation and efforts to prevent adverse health effects in co-workers. Reduction or elimination of exposures to occupational sensitizers and irritants, including through the use of occupational hygiene measures such as ventilation and other engineering controls, help to prevent new cases.
Key Points
Work-related asthma should be considered in all adults with new-onset or worsening asthma.
Diagnosis consists in clarifying the diagnosis of asthma, identifying workplace exposures associated with asthma, and clarifying the temporal relationship between asthma and work.
Triggering exposures and conditions at work and at home should be minimized to the extent possible.
The pharmacological treatment of work-related asthma is similar to treatment of other types of asthma.
