Workplace Chemical Hazards & Asthma

What is Asthma?

Asthma is a chronic condition, meaning it needs to be monitored and controlled over a lifetime. Anyone can get asthma, although it’s usually first diagnosed in young people. The cause of asthma is not known, and currently there is no cure. However, there are many things you can do so you can live symptom-free.

Asthma has no set pattern. Its symptoms:

  • Can be mild, moderate or severe 
  • Can vary from person to person 
  • Can flare up from time to time and then not appear for long periods 
  • Can vary from one episode to the next 

What are the Symptoms of Asthma?

The medical definition of asthma is simple, but the condition itself is quite complex. Doctors define asthma as a “chronic inflammatory disease of the airway” that causes the following symptoms: 

  • Shortness of breath 
  • Tightness in the chest 
  • Coughing 
  • Wheezing 

What Causes Asthma Symptoms?

People with asthma often have trouble breathing when they’re in the presence of what are called “triggers.” When someone with asthma has asthma symptoms, it means that the flow of air is obstructed as it passes in and out of the lungs. This happens because of one or both of the following: 

  1. The lining of the airways becomes inflamed and may produce more mucous. The more inflammation the more sensitive the airway becomes, and the more symptoms. 
  2. The muscles that surround the airways become sensitive and start to twitch and tighten, causing the airways to narrow. This usually occurs if the inflammation is not treated. 

Both of these factors cause the airways to narrow, making it difficult for air to pass in and out of them. The more inflamed the airway the more sensitive the airway becomes. This leads to an increase in breathing difficulty.

What are Asthma Triggers?

An asthma trigger often brings on asthma attacks. A trigger is anything or condition that causes inflammation in the airways, which then leads to asthma symptoms. 

One person’s individual triggers can be very different from those of another person with asthma. But in every case, it’s important to avoid triggers in order to keep airway inflammation to a minimum and reduce the symptoms.

Inflammatory (Allergic) Asthma Triggers

Inflammatory (allergic) triggers can cause inflammation of the lungs’ airways or tightening of the airways’ muscles.  

Inflammatory triggers include:

  • Dust mites 
  • Animals 
  • Cockroaches 
  • Moulds 
  • Pollens 
  • Viral infections 
  • Certain air pollutants 

Symptom (Non-Allergic) Asthma Triggers

Symptom (non-allergic) triggers generally do not cause inflammation, but they can provoke “twitchy” airways, especially if they’re already inflamed. Symptom triggers include: 

  • Smoke 
  • Exercise 
  • Cold Air 
  • Chemical fumes and other strong-smelling substances like perfumes 
  • Certain food additives like sulfites 
  • Certain air pollutants 
  • Intense emotions 

What is Work Related Asthma?

Could your workplace be making you sick? Work-related asthma is the most common occupational respiratory disorder in industrialized countries and the 3rd leading cause of work loss in Canada.  

The costs of unmanaged work-related asthma are high for both employers and workers. If left untreated, work-related asthma can result in disability and job loss. These costs can be largely prevented by incorporating a comprehensive prevention strategy in the workplace. 

If you have asthma, exposures in the workplace can be a cause of asthma symptoms. The symptoms of regular asthma are the same as for work-related asthma. And, for some people being exposed to certain chemicals, irritants or allergens can cause asthma to develop for the very first time. Whether you work indoors or outdoors, the work environment can expose you to irritants and allergens that may be different from what you encounter at home. Early and accurate diagnosis plus changes in the workplace can prevent symptoms from worsening and lead to a healthier work environment for all.   

Work-related asthma falls in one of two main categories:

  1. Occupational asthma 
  2. Work-exacerbated asthma 

Occupational Asthma

The first category of work-related asthma is called occupational asthma. This refers to cases of asthma caused by specific agents in the workplace. The second category is called work-exacerbated asthma. Individuals who have a worsening of their asthma symptoms while at work are said to have work-exacerbated asthma.  

Exposure to workplace irritants or exertion at work may aggravate pre-existing or concurrent asthma, particularly in patients who have moderate or severe asthma, or who are uncontrolled, because they are not receiving optimal treatment. Work-exacerbated asthma represents approximately half of all work-related asthma seen in Canada.  

Occupational asthma can be further divided into two groups:

Sensitizer-induced Asthma

Sensitizer-induced asthma – is caused by sensitization (reaction) to a work-place substance. It can have a latency period of sensitization of weeks to many years. It also represents the majority (over 90%) of Occupational Asthma. Once sensitized to a substance re-exposure at very low levels can trigger an asthmatic response. There are over 300 agents known to cause sensitizer-induced occupational asthma, and the list grows each year.  

Asthma can develop due to a sensitization when it is exposed continuously over a period of time to a substance. Or asthma can be acute and develop suddenly when exposed to a new substance in high levels of exposure. There is no fixed period of time in which asthma can develop. Asthma as a disease may develop from a few weeks to many years after the initial exposure. 

Irritant-induced Asthma 

The second type of occupational asthma is irritant-induced asthma (also called reactive airways dysfunction syndrome, or RADS) which is caused by one specific, high-level exposure. RADS appears after an acute, single exposure to high level of irritating agents (e.g., chlorine, anhydrous ammonia). There is no latency period. The symptoms develop soon after the exposure, usually within 24 hours, and may reappear after months or years, when the person is re-exposed to the irritants. Irritant-Induced Asthma represents a small fraction of occupational asthma (approximately 6%). Re-exposure to low levels of agent generally will not trigger asthma.

How does Occupational Asthma Develop? 

Some workplace conditions seem to increase the likelihood that workers will develop asthma, but their importance is not fully known. Factors such as the properties of the chemicals, and the amount and duration of exposure are important. However, because only a fraction of exposed workers is affected, factors unique to individual workers can also be important. Such factors include the ability of some people to produce abnormal amounts of IgE antibodies. The contribution of cigarette smoking to asthma is not known. However, smokers are more likely than non-smokers to develop respiratory problems in general. 

Exposure to workplace irritants or exertion at work may aggravate pre-existing or concurrent asthma, particularly in patients who have moderate or severe asthma, or who are uncontrolled, because they are not receiving optimal treatment. Work-exacerbated asthma represents approximately half of all work-related asthma seen in Canada.

Chemicals of Irritant Induced Asthma:

  • Ammonia  
  • Chlorine Gas 
  • Smoke/fire 
  • Acids: Sulphuric, Hydrochloric, Phosphoric 
  • Welding Fumes
  • Sealants 
  • Silo gas 
  • Pesticides/Fumigating Fogs 
  • Cleaning agents/removers 
  • Toluene diisocyanate

Who is At Risk to Develop Occupational Asthma?

Here is a table with some occupations that have the highest occurrence of occupational asthma as well as chemicals that most frequently trigger asthma.







Skilled Workers 




Spray Painting 


Metal Workers 
























Reading the Safety Data Sheet for the chemicals you work with and understanding the hazards you are working with is an important step in prevention.