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Sensitizers in the Workplace

By December 7, 2023December 19th, 2023Safety, OSHA/WHMIS/CLP

Sensitizers in the Workplace

Shortly after I first started at ICC, many years ago, I had to visit a client with a co-worker. I offered to drive, but the colleague had an interesting response.

“Only if your car is at least one year old,” he said. “Otherwise, I may have an asthma attack.”

What was the issue? He’d once worked in the automotive industry and had developed an allergy to a family of chemicals called isocyanates. These are found, among other places, in the foam of car seats. Until a car had aired out for at least a year, there would still be enough isocyanate vapour in the air to trigger a reaction.

Allergies, or hypersensitivities as they’re often called, are often looked at as relatively trivial, but they can be life-threatening. Even less serious sensitivities may force workers out of jobs handling specific chemicals. Therefore, countries using the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) system for workplace safety require that suppliers of chemicals known to have an elevated risk of causing sensitization must be clearly identified.

The Basics – What Is Sensitization?

Sensitization has been described as “an immunologic process that occurs within our bodies in response to repeat exposure to a sensitizing substance.” Sometimes, exposure to a chemical can cause the body to treat molecules of that chemical as foreign pathogens, producing an autoimmune reaction. This reaction can range from relatively minor, such as a slight rash or a runny nose, up to more serious ones, such as an asthma attack blocking someone’s airways. Typical hypersensitivity symptoms include:

  • Anaphylactic reaction – a life-threatening reaction that may result in bronchospasm, swelling of the tissues of the throat and larynx, severe drop in blood pressure, nausea and vomiting, and shock.
  • Allergic asthma – typical asthma reactions include cough, shortness of breath, and difficulty breathing. Severe reactions may result in obstruction of airways and be life-threatening.
  • Allergic rhinitis – this is the typical “hay fever” collection of symptoms, such as stuffy or blocked nose, sneezing, reddened or swollen nasal passages, and itchy or watering eyes. While not immediately life-threatening, this can impact job performance due to discomfort.
  • Atopic dermatitis or eczema – skin reactions (often from direct contact with the chemical but sometimes also from inhalation or other modes of exposure) can include rash, itching, redness, and swelling. Severe reactions can lead to hives, plaque, or blistering and peeling of the skin.

But unlike other toxic reactions, sensitization doesn’t follow a standard “dose-response curve,” where most people tend to get sick on exposure to large enough doses. Once someone has developed the immune response, tiny amounts of the chemical can cause a massive overreaction in the body, up to the infamous “anaphylactic shock.” Other people, without such sensitivity, may not show any reaction to exposures that make the sensitized person seriously ill.

The mechanisms of developing sensitization are not yet fully understood. They may be at least partially genetic – for example, if your parents have a lot of allergies, you are more likely to develop them yourself. But there are other factors, such as early exposures to various triggers, that can also create an increased likelihood of sensitization. One writer comments:

“Why this happens to such a small subset of the population is unknown. Interestingly, several studies have indicated that allergen-specific sensitization differs by sociodemographic and regional factors and that the probability of allergenic sensitization decreases with age. There also appears to be a hereditary factor in determining your risk of allergen-specific sensitization.”

This makes the study of sensitizers (allergens) in the workplace difficult. Not everyone is going to be sensitized. Usually, only a small proportion of workers will have a bad reaction, and other workers will continue without ill effect. So, sensitizers likely to cause problems in the workplace are evaluated in two possible ways:

  1. Human epidemiological studies – in these studies, large groups of workers are evaluated for reports of sensitization. Workplace chemicals with a significantly higher than normal incidence of allergies may be sensitizers. But it isn’t that easy. Most workers are exposed to multiple chemicals at work. If a cluster is detected, there may be many possible suspects. This takes dedicated research to untangle.
  2. Animal studies – these studies involve exposing animal test subjects to potential sensitizers and looking for evidence of reaction either by visible symptoms or biochemical markers of an allergic reaction. In the GHS, they mention using the Local Lymph Node assay, the Guinea Pig Maximalization test, and the Buehler assay, as well as a screening test called the Mouse Ear Swelling test, which is just what it sounds like. Because these tests are more controlled than epidemiological studies of humans, they can often be easier to interpret.

The Canadian Center for Occupational Health and Safety (CCOHS) admits there is a “lack of understanding of the underlying toxicological mechanisms, confused terminology, the absence of internationally accepted experimental tests, inconclusive clinical data, and doubt concerning … different exposure patterns and routes” with regards to studying allergic responses such as occupational asthma. This has hindered the understanding of how sensitizers affect the workplace.

What Chemicals Are Frequent Sensitizers?

Theoretically, an individual can be sensitized to almost any chemical, but some have a much higher likelihood of causing sensitization. According to reports, “[a]pproximately half of occupational ACD [allergic contact dermatitis] cases are due to rubber, nickel, and fragrances.” Latex allergies, for example, have become a serious issue among healthcare workers.

Other chemicals that are known to be associated with increased allergic response in workers include:

  • Biological substances, such as mold, pollen, nut oils, and animal dander
  • Wood dusts, especially from species such as cedar, ash, beech, and spruce
  • Formaldehyde
  • Toluene diisocyanate and related chemicals in the isocyanate family
  • Plastic precursors, such as acrylates and methacrylates
  • Metal salts, particularly chromates and platinum compounds
  • Dyes, such as used in hairdressing
  • Photographic developing chemicals

As you can see, many industries are affected by sensitizers. And even if your workplace doesn’t use any of the above chemicals, certain individuals may develop allergic reactions to materials that aren’t on the above list.

What Can You Do About Sensitizers in the Workplace?

There are, of course, different responsibilities for employers versus workers. If you’re an employer, you should develop a comprehensive protocol for sensitizers, including:

  1. Review the safety data sheets (SDSs) for products you’re using in the workplace. Under regulations such as OSHA (Occupational Safety and Health Act) in the United States and WHMIS (Workplace Hazardous Materials Information System) in Canada, SDSs must indicate if there’s any evidence the product is a sensitizer. Remember, however, that even if this is not indicated, some workers may develop allergies to specific chemicals.
  2. If sensitizers can be replaced with less hazardous chemicals, do so.
  3. If the use of sensitizers cannot be avoided, develop a plan for reducing exposure to such chemicals. This may include industrial hygiene measures such as increased ventilation in general work areas and the use of sensitizers only in enclosed or well-ventilated areas. As a last resort, protective equipment such as gloves and respirators may be used, but not unless all other exposure control measures are unable to reduce the risk. Exposure control plans should be in writing.
  4. Educate your workers about sensitization risks.
  5. Investigate any evidence of workers developing symptoms of sensitization, such as rashes, watering eyes, or persistent coughing. Even minor symptoms may indicate a more serious reaction is likely to occur if exposure persists.
  6. Ensure that emergency responders, such as first aiders, are familiar with how to identify life-threatening reactions, such as anaphylactic shock or airway obstruction, and have been instructed how to respond if they see someone in difficulty.

Workers can also use labels and SDSs to determine if chemicals could put them at risk of developing sensitization. Familiarize yourself with the typical symptoms of respiratory and dermal sensitization. Remember that allergies don’t usually show up on the first exposure to a chemical. You may have worked with a substance for months or years before the first signs of sensitization appear, but once they do, even tiny exposures can result in painful or even life-threatening reactions.

Steps to help protect yourself include:

  1. Always check labels and SDSs for new products.
  2. Consult any written workplace safety plans.
  3. Always follow company procedures to limit exposure to sensitizers. Don’t let “familiarity breed contempt” and assume that a reaction couldn’t develop with a chemical you’ve handled for some time.
  4. Be scrupulous about cleaning up spilled chemicals and laundering work clothes.
  5. If you notice any symptoms that could be due to allergies – skin irritation, eye irritation, coughing, or even digestive reactions such as nausea or diarrhea – that seem to occur in conjunction with exposure to certain chemicals, do not ignore them. You can’t “push through” sensitization by repeated exposure. That will likely lead to a worsening of the sensitization reaction. Consult medical professionals who can help narrow down what you are sensitive to.
  6. Eliminate exposure to as many sensitizers from your life as possible, both at work and at home.


Do you have questions about how sensitizers are regulated in the United States and Canada? We can help you with OSHA and WHMIS questions on toxic chemicals such as sensitizers. Contact ICC Compliance Center here at 888-977-4834 (Canada) or 888-442-9628 (U.S.) and ask for one of our Regulatory Experts. We can advise you on how to comply with regulations to keep the workplace allergy-free.

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Barbara Foster

Barbara Foster graduated from Dalhousie University with a Master’s degree in Chemistry and a Bachelor’s degree in Education. As one of ICC Compliance Center’s most senior employees, she has worked in the Toronto office for the past three decades as a Regulatory Affairs Specialist and Trainer. She is fluent in various US, Canadian, and international regulations involving transportation, including TDG, 49 CFR, ICAO, IMDG, and the ADR/RID. She also specializes in the hazard communication standards of OSHA, WHMIS, CCCR, and the Globally Harmonized System for Classification and Labelling (GHS). Barbara is the author of ICC’s TDG Clear Language Driver and Handler’s Guide. Currently, she is a participant on the Canadian General Standards Board committee where she creates training standards for transportation of dangerous goods in Canada and is a past Chair of the Dangerous Goods Advisory Council.