Irritant-Induced or Occupational Asthma

Man about to use asthma inhaler
Irritant-induced asthma. Martin Barraud / Getty Images

Irritant-induced asthma (or IIA for short) is a type of occupational asthma caused by exposure to gas, fumes, vapors or inhaled particles. A similar condition is reactive airway dysfunction syndrome (or RADS for short).

These illnesses are classified as occupational asthma because many of the exposures to irritant substances that lead to RADS and IIA occur in the workplace. However, exposures to triggering irritants can happen in the home or public areas, too; therefore, RADS and IIA are not always work-related.

RADS and IIA were first recognized as distinct illnesses in 1985, and issues concerning their diagnosis have attracted some controversy. Establishing a definite connection between a person's exposure to an irritant and a person's asthma symptoms is not always easy. Additionally, differentiating RADS and IIA from other types of asthma can be difficult.

The Difference Between RADS and IIA

Generally speaking, RADS is diagnosed when a person (without previously diagnosed asthma) develops asthma symptoms after a sudden (often accidental) and significant exposure to an irritant. After the first exposure, a person with RADS has respiratory symptoms that occur immediately (within 24 hours).

RADS is believed to be caused by a direct toxic impact on the cells that line the airway. The irritation then triggers an inflammatory response which is distinct from an allergic response to repeated exposures–the pathway in most people with asthma.

The controversy about the diagnosis IIA or low-dose RADS lies in the proposed mechanism of the disease. The question remains whether there can be direct damage to the cells from prolonged lower level exposure, without an allergic component.

A UK-based expert panel, convened in 2006, adopted the term "acute irritant-induced asthma" rather than RADS, and while they proposed the term "low dose irritant-induced asthma" instead of low-dose RADS–here continued to be disagreement on whether this entity exists.

Inflammation Due to Airway Irritation

When people are exposed to a large amount of an irritant, the tissues that line their airways are damaged. The damage is similar to a burn, with a loss of surface cells and small areas of bleeding and swelling below the surface.

In comparison, an allergic reaction is different because it involves the response of the body's immune system. The airways of people with chronic lung disease due to RADS will thicken and show fibrous deposits, and the airway tissues are effectively scarred.

Diagnosis and Treatment 

There are three main criteria for recognizing RADS and IIA

  • Airway distress with wheezing, coughing, and shortness of breath that occurs after exposure to an irritant (such as chlorine, cleaning agents or smoke). In RADS, this occurs soon after a large exposure; in IIA, this occurs after smaller, multiple exposures.
  • No history of prior asthma complaints.
  • Symptoms persist beyond the initial exposure.

With RADS, many people describe an immediate burning sensation in the nose and throat at the time of exposure, with the airway symptoms either immediately afterward or within hours.

When someone has already had a high-level exposure to an irritant, and no previous history of lung complaints, symptoms are more easily attributable to their exposure. However, when a person has already had prolonged or multiple exposures, it is more difficult to prove that these symptoms were a direct cause of an irritant.

If a physician suspects RADS or IIA, she will conduct a thorough history and physical exam. The physician may order pulmonary function tests to determine how or if the lungs have been affected.

Often, a person who has RADS will show less improvement in symptoms after using certain asthma medicines (bronchodilators such as albuterol) than people with asthma.

Immediately after exposure, oral steroids are prescribed to decrease the inflammation in the airway. Inhaled steroids are prescribed if the symptoms persist.

How Much Is Too Much?

It is unclear how frequently inhalation of irritants cause RADS and IIA. Studies of employees involved in large chemical exposures–such as chlorine, acetic acid or mustard gas leaks–have shown that 11% to 57% of those people who were exposed developed RADS. In one study of firefighters who were exposed to debris from the World Trade Center on September 11, 16% were diagnosed with RADS 1 year later. Another study of all employees with occupational asthma in 4 states found that RADS represented 14% of all documented occupational asthma cases.

Many professions put people at greater risk for irritant exposures that can cause RADS and IIA. Irritants that are frequently cited as being implicated in the development of these illnesses include various acids, bleaching agents, cleaning agents, chlorine gas, diesel exhaust, formaldehyde, sulfur dioxide, and isocyanates, which are often used in plastics and adhesives.

Anyone who works with dangerous substances should be made aware of the risks. The Occupational Safety and Health Administration (OSHA) mandates that employers must have safety measures in place that include protective equipment, education, and instructions on what to do if there is an accidental exposure. If you suspect that your employer is not in compliance with these regulations, contact your local OSHA office.

Beyond the medical consequences that can interfere with regular activities, there can be social and financial consequences of RADS and IIA as well. Physicians and researchers continue to search for definitive ways of diagnosing these conditions due to the professional and legal standing it would give patients affected by them. For people who are exposed and injured in the workplace, an accurate diagnosis is crucial for obtaining compensation and benefits.

Content edited by Naveed Saleh, MD, MS, on 2/11/2016.

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