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Why You Should Not Use Cedar Shavings As Pet Bedding


or, What's Wrong with Cedar Shavings?
by R. Kelly Wagner

(c) 1996, revised (c) 1999

Some pet owners have asked why we do not recommend cedar shavings or pine shavings for use as a bedding material or litter-box filler for guinea pigs, rabbits, or other small pets. There are two big reasons:

* The scented oils in the shavings can affect the animal's metabolism and liver function, and possibly induce cancer or precancerous lesions, especially on the liver;

* The shavings can cause allergic reactions and/or asthma, and trigger asthma attacks, in humans and in the animals.

As alternatives, pet owners may wish to try aspen shavings as bedding, or Carefresh, a recycled-wood-pulp bedding/litter. There are also other alternative fillers available in different parts of the country - other brands of recycled paper fillers, dried orange-peel fillers, and so on. Try several types to find one (or a combination) which your pet likes to use and which controls odor adequately for your household. At the end of the article, there are more suggestions for bedding.

Below are various articles and excerpts from articles, to give the background for both of the problems above.

First, details on the dangers of pine and cedar to the animal metabolism and liver are shown below, taken from a government guide for handling laboratory animals. Here are the exerpts and citations from:

“Guide for the Care and Use of Laboratory Animals” published by the National Research Council (1) edition released 1/2/96.

Softwood (2) beddings have been used, but the use of untreated softwood shavings and chips is contraindicated for some protocols because they can affect animals’ metabolism (Vesell 1967; Vessell and others 1973, 1976). Cedar shavings are not recommended, because they emit aromatic hydrocarbons that induce hepatic microsomal enzymes and cytotoxicity (Torronen and others 1989; Weichbrod and others 1986, 1988) and have been reported to increase the incidence of cancer (Jacobs and Dieter 1978; Vlahakis 1977). Heat treatments applied before bedding materials are used reduce the concentration of aromatic hydrocarbons and might prevent this problem. (3) Manufacturing, monitoring, and storage methods used by vendors should be considered when purchasing bedding products.

Bedding should be transported and stored off the floor on pallets, racks, or carts in a fashion consistent with maintenance of quality and minimization of contamination. During autoclaving, bedding can absorb moisture and as a result lose absorbency and support the growth of micro-organisms. Therefore, appropriate drying times and storage conditions should be used.

... Agents designed to mask animal odors should not be used in animal housing facilities (4)... they expose animals to volatile compounds that might alter basic physiologic and metabolic processes. ... Rabbits and some rodents, such as guinea pigs and hamsters, produce urine with high concentrations of proteins and minerals. Minerals and organic compounds in the urine from these animals often adhere to cage surfaces and necessitate treatment with acid solutions before washing. (5)

* * *

OK, that was the technical details. For most people, the rest of the Guide is not relevant, but those of you with large numbers of animals may wish to read more about how big labs handle feeding and cleaning large quantities of animals. Some knowledge of scientific protocol and technical lab equipment is assumed; the Guide is not written in language for pet owners. You can order a copy by calling 1-800-624-6242. It’s $9.95 plus $4.00 shipping and handling. (Please don't all call at once - the government is not set up to take a lot of retail orders for this sort of institutional material.) They also have books on Recognition and Alleviation of Pain and Distress in Laboratory Animals, Infectious Diseases of Mice and Rats, Immunodeficient Rodents, and other exciting titles.

Notes from Kelly:
1. This is an arm of the National Institutes of Health, in conjunction with the Dept. of Health and Human Services, the US Dept. of Agriculture, and the Dept. of Veterans Affairs. It is the rule book used by anybody who does research using federal govt. grants. It is considered as a primary reference on animal care and use.

2. Pine and cedar are softwoods.

3. The Guide mentions that if you change bedding every day or more, there is less risk from beddings, such as pine, and also discusses the effect of air flow on bedding: the better the ventilation of the cages and the room they are in, the less risk any bedding poses.

4. This means, don't use any litters with artificial scents or perfumes, or "air fresheners" added.

5. Regarding the removal of urine from cage surfaces, many people use bleach, as the strongest and fastest cleaner for surfaces. I’ve also found hydrogen peroxide does a good job of loosening dried minerals and urine seemingly enameled onto the bottom of a cage or litter pan, and doesn't smell as strong as bleach.


Cedar shavings also have respiratory effects on both animals and humans. These effects can including triggering allergic attacks in some people, and triggering asthma attacks in people who already have asthma. Repeated exposure to cedar may even cause asthma in people who did not previously have it. Below, there are several articles from medical journals documenting "occupational asthma" in people who work with cedar trees and sawdust for a living.

I'd also like to add some empirical evidence that I've collected. (Although this is not as good as a scientific study, it is data that can add support to the existing arguments on why not to use cedar.) I run Guinea Pig Rescue of Austin. This means that I get calls from people who want to surrender their guinea pigs, as well as taking in guinea pigs from local animal shelters that only have facilities to keep cats and dogs. When I get calls from people who want to give up their guinea pigs, I ask them why. Some are moving, sometimes a family has circumstances that mean they can no longer care for a guinea pig - and sometimes, the reason is that they think they are allergic to their guinea pig. When someone tells me this last as their reason, the very next thing I ask is what kind of bedding they use for their pet. In the past 2 years, 16 of the calls I've gotten have been from people who gave allergies as their reason. Of those 16, when I asked the bedding question, 13 of them responded that they used cedar shavings. What I did in each of those cases was make the following suggestion:

Go buy a bag of Carefresh or aspen shavings. Throw away all the cedar shavings, and use the new bedding in your guinea pig's cage for a week. At the end of one week, if you are still allergic to your guinea pig, I will then not only take the guinea pig, I will pay you back for the full bag of Carefresh or aspen, even though it will be partly used up.

Well - after one week, twelve (12) of those 13 people called back to say that they (or their family member) were no longer allergic to the guinea pig!! That is, it was actually the cedar shavings causing respiratory allergy symptoms; when the cedar was removed, and a bedding without aromatic phenols substituted, their respiratory reactions decreased or disappeared.


Here are some of the technical articles about cedar (and other aromatic softwoods) and asthma/allergies:


Articles on Asthma in humans from cedar

Med Pr 1993;44(3):277-88 [Biological effect of wood dust].[Article in Polish] Maciejewska A, Wojtczak J, Bielichowska-Cybula G, Domanska A, Dutkiewicz J, Molocznik A Zakladu Aerozoli Instytutu Medycyny Pracy, Lodzi.

The biological effect of exposure to wood dust depends on its composition and the content of microorganisms which are an inherent element of the dust. The irritant and allergic effects of wood dust have been recognised for a long time. The allergic effect is caused by the wood dust of subtropical trees, e.g. western red cedar (Thuja plicata), redwood (Sequoia sempervirens), obeche (Triplochiton scleroxylon), cocabolla (Dalbergia retusa) and others. Trees growing in the European climate such as: larch (Larix), walnut (Juglans regia),oak (Quercus), beech (Fagus), pine (Pinus) cause a little less pronounced allergic effect. Occupational exposure to irritative or allergic wood dust may lead to bronchial asthma, rhinitis, alveolitis allergica, DDTS (Organic dust toxic syndrome), bronchitis, allergic dermatitis, conjunctivitis. An increased risk of adenocarcinoma of the sinonasal cavity is an important and serious problem associated with occupational exposure to wood dust. Adenocarcinoma constitutes about half of the total number of cancers induced by wood dust. An increased incidence of the squamous cell cancers can also be observed. The highest risk of cancer applies to workers of the furniture industry, particularly those dealing with machine wood processing, cabinet making and carpentry. The cancer of the upper respiratory tract develops after exposure to many kinds of wood dust. However, the wood dust of oak and beech seems to be most carcinogenic. It is assumed that exposure to wood dust can cause an increased incidence of other cancers, especially lung cancer and Hodgkin's disease. The adverse effects of microorganisms, mainly mould fungi and their metabolic products are manifested by alveolitis allergica and ODTS. These microorganisms can induce aspergillomycosis, bronchial asthma, rhinitis and allergic dermatitis.


Clin Exp Allergy 1998 May;28(5):537-44 Exposure-response relationships of occupational inhalative allergens. Baur X, Chen Z, Liebers V Research Institute for Occupational Medicine (BGFA), Institute at the Ruhr-Universitat Bochum, Germany.

Only a few threshold limit values exist at present for allergens in the workplace known to cause bronchial asthma. This contrasts with the great number of occupational asthma cases observed in industrialized countries. Recently published studies provide clear evidence for exposure intensity response relationships of occupational allergens of plant, microbiological, animal or man-made origin. If allergen exposure levels fall short of determined limit values, they are not associated with an increased risk of occupational asthma. Corresponding data are available for wheat flour (1-2.4 mg/m3), fungal alpha-amylase (0.25 ng/m3), natural rubber latex (0.6 ng/m3), western red cedar (0.4 mg/m3) and rat allergens (0.7 microg/m3). It is suggested to stipulate legally binding threshold limit values (TLV/TWA) on this basis in order to induce more effective primary preventive measures. If no reliable data on the health risk of an occupational airborne noxa exist, the lowest reasonably practicable exposure level has to be achieved. Appropriate secondary preventive measures have to be initiated in all workplaces contaminated with airborne allergens. Verified exposure-response relationships provide the basis for risk assessment and for targeted interventions to reduce the incidence of occupational asthma also in consideration of cost benefit aspects. 'Occupational asthma is a disease characterized by variable airflow limitation and/or airway hyperresponsiveness due to causes in a working environment. These causes can give rise to asthma through immunological or non-immunological mechanisms. Up to 15% of all asthma cases are of occupational origin or have at least a significant causal occupational factor. According to the New Zealand part of the European Respiratory Health Survey, an increased risk of asthma prevalence was found for several occupations such as laboratory technicians, food producers, chemical workers, plastic and rubber workers. The Spain part of this study comprising 2646 Spanish subjects showed an asthma risk to be attributed to occupational exposures between 5 and 6.7%. Main asthma-inducing agents in the workplace are flour, grain and feed dust, animal dander/urinary proteins and isocyanates. Further, several inhalative irritants such as chlorine, acid or alkaline aerosols play a pivotal role. Many low molecular weight chemicals have irritative as well as allergenic effects on the airways, e. g. isocyanates and acid anhydrides. In addition to chronic or repetitive exposures, also singular accidental exposure to high concentrations of irritative or toxic airborne substances can cause occupational asthma. This condition is frequently called reactive airways dysfunction.


Bull Acad Natl Med 1991 May;175(5):703-12; discussion 712-5 [Occupational asthma: current and future perspectives. The point of view of an expert]. [Article in French] Choubrac P

Occupational asthma remains a difficult problem for physicians and for experts. The prevalence of occupational asthma is underestimated and depends on industrial agent and conditions of work. Diagnosis is made based on detailed description of the patient's work environment, on skin and serological tests, and on lung function tests including non-specific bronchial provocation tests. Rhinomanometry, and peak flow rate measurements may also be useful. Bronchial provocation tests should be performed by experienced staff in a hospital setting with facilities for resuscitation. The prognosis of occupational asthma is variable: --some patients with short and limited exposure may fully recover if their disease is early recognized and appropriate measures are taken; --however, many patients do not recover completely after removal of the responsible agents. Clinical symptoms and bronchial hyperreactivity persist and respiratory insufficiency may develop. The patterns of occupational asthma are changing rapidly, in parallel with industrial evolution: nowadays, bakers's asthma is less frequent than it used to be. Asthma triggered by wood dust and in particular western red cedar (which is exported all over the world) is increasingly recognized. Isocyanates and, in particular toluene isocyanate, are widely used in plastics and paints. Preventive measures have succeeded in decreasing the incidence of asthma caused by exposure to isocyanates. Computer industry has recently developed in many countries. It requires the use of numerous hazardous and highly toxic materials that are potentially responsible for occupational asthma; attention should be given to respiratory diseases especially in industrializing countries (such as Eastern Asian countries). Preventive measures include safety rules, replacement of harmful materials by less toxic agents and detection of susceptible workers. Regulation must be defined under experts' control to continuously match the rapid changes in modern industry.



For more information, try these sites:

Respiratory Toxicity of Cedar and Pine Wood
Environmental Factors Affecting Laboratory Animals



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Fed Proc 1976 Apr;35(5):1125-32 Environmental and genetic factors affecting the response of laboratory animals to drugs. Vesell ES, Lang CM, White WJ, Passananti GT, Hill RN, Clemens TL, Liu DK, Johnson WD


Only some of the diverse factors that can affect drug disposition and response in laboratory animals have been identified at the present time. These numerous factors contribute to large day-to-day variations that have become a major problem impeding investigation of drug disposition and response in laboratory animals. Although these variations render many experiments difficult to interpret and produce large discrepancies in the literature, few published investigations using laboratory animals provide sufficient details to permit replication of the studies under similar conditions with respect to these variables. Thus, the importance of these variables in affecting results is apparently insufficiently recognized at present. Two commonly overlooked variables affecting the activity of hepatic microsomal enzymes (HME) in rodents and hence the rate at which rodents eliminate from their bodies many foreign compounds are the bedding under the wire mesh cage and the relative cleanliness of the environment. Numerous chemicals present in relatively low concentrations in the environment of the animal room can significantly alter HME activity. Representative of these chemicals are aromatic hydrocarbons in cedarwood bedding, eucalyptol from aerosol sprays, and chlorinated hydrocarbon insecticides, each of which induces HME activity, whereas ammonia generated from feces and urine accumulated in unchanged pans under cages may inhibit HME activity. Chloroform, identified as an environmental contaminant of the water and air of certain cities, exhibits sex and strain differences with respect to toxicity (LD50) in mice. After intraperitoneal injection, twice as much chloroform accumulated in the kidneys of males from the sensitive strain (DBA/2J) as from the resistant (C57BL/6J) strain. First