November December, 2004





Questions and Answers About Western Red Cedar and Asthma

By Christy Curwick, MPH, Wash. Dept of Labor

I recently had the opportunity to tour several cedar mills in Washington state, and have spoken with plant and safety managers about western red cedar asthma. From these conversations, I’ve come to realize that while many in the industry have heard of western red cedar asthma, it remains a bit of a mystery and may be regarded with little concern and possibly a bit of skepticism. My goal in writing this article is to clear the air, so to speak, by outlining the facts of western red cedar asthma — both what is currently known and what remains to be learned. But first, I’d like to illustrate this issue by describing one worker’s experience with western red cedar asthma.

Case Study
A male worker in his early thirties developed symptoms of shortness of breath and itching approximately one year after he started working in a sawmill that primarily processed western red cedar. His symptoms were mild and sporadic at first, and he noted that they would clear over the weekends and worsen throughout the workweek. He continued to work at the mill for about two more years, during which time his symptoms worsened and he finally sought treatment. His physician conducted several tests and diagnosed him with allergies and asthma caused by western red cedar. At that time, his physician removed him from work and a workers’ compensation claim was filed. In the end, the worker underwent vocational retraining, as he could no longer work around cedar. This claim incurred workers’ compensation costs of over $63,000, which included reimbursement for over 1,300 lost workdays.

What is asthma?
Asthma is a chronic lung disease in which the airways become constricted and inflamed and excess mucous is produced in response to various triggers. As a result, breathing becomes difficult. Symptoms of asthma include chest tightness, shortness of breath, wheezing, and coughing.

How does western red cedar cause asthma?
Western red cedar contains a number of chemical extractives — these are non-structural components of the wood that give it color and smell. One of western red cedar’s many chemical extractives is called plicatic acid. Plicatic acid can cause an allergic reaction in some workers (called sensitization) that results in asthma.

How common is western red cedar asthma?
The proportion of workers exposed to western red cedar dust who end up developing occupational asthma has been studied1,2 and shown to range from between 2-24 percent, depending upon the level of cedar dust in the air and the diagnostic criteria used. These studies clearly demonstrated that the risk for developing asthma increased as western red cedar dust exposures increased.

Is there a safe level of western red cedar dust?
Unfortunately, there is no known safe level of exposure for western red cedar dust. What is known is that reducing the level of western red cedar dust can reduce the prevalence of occupational asthma. For example, in one cedar mill, 15 percent of workers exposed to dust levels between 2 and 6 mg/m3 had western red cedar asthma, while only 6 percent of workers exposed to levels less than 1 mg/m3 had asthma symptoms3.

Are some workers more likely than others to develop western red cedar asthma?
Yes, but there is no way to predict who will become sensitized to western red cedar dust, so it is important to limit exposures to all workers. Neither smoking, nor a previous history of allergies, has been shown to increase a worker’s risk of developing western red cedar asthma.

How can western red cedar asthma be prevented?
The first step in preventing western red cedar asthma is hazard assessment. Managers should identify the areas in the facility that produce the greatest amount of dust. Next, steps should be taken to reduce the levels of wood dust as much as possible. Following is a prioritized list of possible ways to reduce wood dust exposures – those listed first are the most effective: Engineering Solutions — Provide controls to reduce the level of dust that reaches the workers. Examples include:
•Enclose machines and/or specific operations with a ventilation system to isolate workers from the wood dust.
•Install local exhaust ventilation to remove dust before it enters the work environment.
•Consider the feasibility of using wet-work methods to reduce airborne dust. Administrative Controls — Encourage and enforce safe work practices.

Examples include:
•Train workers on the hazards of western red cedar dust and ways to minimize exposures.
•Provide washing facilities and changing areas to decrease take-home exposures to cedar dust.
•Ensure that the facility is cleaned regularly. Personal Protective Equipment (PPE) — PPE, including coveralls and approved respirators should always be the last line of defense and should not be considered primary control methods.

How is work-related asthma diagnosed?
Workers with questions about their breathing should see a doctor immediately. A physician should conduct tests to determine if the worker has asthma, and not some other kind of lung condition. If a diagnosis of asthma is confirmed, the doctor should then perform further testing to determine whether the asthma is work-related. Asthma is a serious disease and could severely affect a person’s health or even cause death. Early diagnosis can lead to a better health outcome.

Western red cedar asthma can be a serious and costly disease. Primary prevention of western red cedar asthma relies on reducing the levels of cedar dust in the work environment as much as possible. While there is currently no known safe level of cedar dust exposure, research has shown that reducing the levels of cedar dust will lead to decreased prevalence of occupational asthma. Engineering controls, such as enclosing operations and installing and maintaining local exhaust ventilation systems, are the most effective methods for reducing the levels of cedar dust that reach the worker.


1. Chan-Yeung M. (1993). Western Red Cedar and Other Wood Dusts. In Bernstein L, Chan-Yeung M, Malo J, Bernstein DI (eds). Asthma in the Workplace. New York: Marcel Dekker. 503-531.
2. Demers PA, Teschke K, Kennedy SM. (1997). What to Do About Softwood? AReview of Respiratory Effects and Recommendations Regarding Exposure Limits. American Journal of Industrial Medicine, 31:385-398.
3. Vedal S, Chan-Yeung M, Enarson D, Fera T, Maclean L, Tse KS, Langille R. (1986). Symptoms and pulmonary function in western red cedar workers related to duration of employment and dust exposure. Archives of Environmental Health, 41:179-183.

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This page was last updated on Wednesday, December 29, 2004