top of page




If you’re still disputing that those cheap kiln dried pine shavings aren’t as harmful to your hamster as what we always harp on about, read the two articles below.

1. ~ from Hamster Hideout Forum


Cedar and Pine: Why you should avoid it.
A special thanks to Taxonomist for her contributions to this article.


We have all read the warnings about the use of cedar or pine as substrates - it’s dangerous to our little friends’ health and can cause permanent damage. But that leaves a lot of us with questions of why it hurts them or how it’s more dangerous than other substrates. I will explain as best I can, using citations of medical and scientific articles rather than circumstantial discussions and “how-to” articles.

Why cedar?
Cedar itself contains a component called “plicatic acid,” which is unique to cedar - all species of cedar. This acid is a natural fungicide - meaning it protects the wood from fungus - and is what makes cedar a great gardening and fencing product without needing chemical treatments to resist rotting. There are other natural compounds in cedarwood that are more potent fungicides, but plicatic acid is about 8 to 10 times more abundant than any of the others. (Many of those other compounds are toxic in their own rights, but for the purpose of this article I will limit myself to plicatic acid for the time being.)
Source 1:


Why pine?
Pine doesn’t contain plicatic acid, but it does contain “abietic acid.” Pine is a species of conifer tree, and all species of conifer trees contain abietic acid - this includes spruce, fir, cypress, juniper, yew, and the aforementioned cedar. Abietic acid is commonly used in solder flux (a product used in soldering microchips and copper pipes), in rosin (used by violinists), and in some cleaning products (Pine Sol.) OSHA has classified abietic acid as a skin and respiratory irritant, so that industries where workers are exposed to the acid are required to monitor exposure levels.
Source 2:


How does exposure occur?
The most common ways to get exposed to either of these acids is through physical content or through inhalation. In Source 3, samples of lung and tracheal (windpipe) tissue from both rats and humans were exposed to plicatic acid and abietic acid. They tested for both dose-dependent and time-dependent results, meaning that they tested a variety of doses and evaluated the progress over an extended time period. The result was lysis (disintegration) of cells, and then sloughing (shedding) of the dead cells, for both acids, both short-term from high doses and long-term from low doses. For example, sloughing also happens on burn patients, leaving the inner layers of skin exposed to infection and probable scarring.
Source 4 is a discussion of asthma in humans as a result of exposure to plicatic acid. The study followed individuals in the woodworking industry. Those who reacted had high levels of certain antibodies, and those who did not react didn’t have the antibodies, which showed that the asthma was an immune system response to cedar exposure. Of the 75 individuals who left the woodworking industry (and so were no longer exposed to cedar), only half of them actually stopped having asthma symptoms after 3 years.
Source 5 is an article for the International Agency for Research on Cancer, analyzing a variety of earlier studies involving carcinogenicity (cancer-causing) of wood dust. One cited study discusses how pine, alder, and cedar were significantly more cytotoxic (cell-killing) than the other studied wood, aspen, but bleached cellulose materials (paper) were nontoxic even at incredibly high doses. A second cited study compares abietic acid and plicatic acid exposure, concluding that both are cytotoxic, though plicatic acid is more toxic even at significantly lower levels.
Source 6 is an evaluation by the National Toxicology Program of wood dust. Western Red Cedar is regulated by OSHA separately from other woods for inhalable wood dust limits. Wood dust in general is classed as a Known Human Carcinogen, though sensitivities to softwoods in particular (cedar, pine, fir, hemlock, etc.) are noted.
Lastly, Source 7 is a scholarly article about the toxicity of pine and cedar in small animals. The article acknowledges that most studies have focused on occupational exposure in humans, rather than bedding in small animals, though the fact that plicatic/abietic acids kill cells still holds true regardless of the method of exposure. In fact, considering that small animals on pine or cedar bedding are in near-constant contact with the offending products, it could be surmised that they would receive more direct exposure.
Source 3:
Source 4:
Source 5:
Source 6: (unfortunately page no longer available)
Source 7:


What about phenols?
Phenols are aromatic compounds that are known to be toxic and caustic (causes acid burns) in higher concentrations, and are used in a variety of industries. In lower concentrations they can be used as antiseptics, such as mouthwash or Lysol... even then, we all learned as children that we shouldn't drink mouthwash. Phenols are volatile, with a low molecular weight, meaning that they become airborne very easily. They are very common, especially in any strong-scented wood.


What about kiln-drying?

Contribution by Taxonomist:

Contrary to what its name might suggest, abietic acid is a very stable solid.  The melting point of abietic acid is between 282 - 311F(Source 10), depending on purity. Its boiling point is absurdly high at about 823F. This means that for abietic acid to be removed from pine wood, the wood would have be heated to at least 282F to allow the abietic acid to melt and ooze out. Even this would not necessarily guarantee removal, as wood is porous and capable of holding liquid like a sponge.

The stability of abietic acid presents a problem regarding kiln drying.  Kiln drying is done at rather low temperatures, to prevent damage to the wood.  The standard kiln drying temperature for most pine species is no higher than 180F (range 100F - 180F, Source 11).  This is much too cool to even melt, much less boil, abietic acid from pine wood.

It doesn't seem that kiln-drying has any effect on the abietic acid content of the wood.  Kiln-drying would not melt or evaporate the abietic acid out of the wood (as is so commonly believed)--it would remain as a solid, unaffected by the process.



As an engineer part of my education was with treatment systems, such as with wastewater and airborne contaminants. What you will always find is that you can never get rid of the contaminant. You can reduce it, sure, but never eliminate it. As your “elimination process” works, over time there will be decreasing rates of return. So if you filter air from a contaminated room for 60 minutes, in that first 30 minutes you’ll catch more contaminants than you will in the second 30 minutes. If we filtered that room for 365 days, there would still be contaminant in there that we haven’t yet caught. Well, it’s the same for kiln-drying - after a little while the amount of work you put in to remove the offending substance just doesn’t balance out with how much you actually remove.

But remember: kiln-drying is focused on removing water, not phenols and not abietic acid. Even though some lightweight compounds evaporate during the kiln-drying process, not all will, and that is the discerning point here. How much depends on how much was there in the first place, the temperature of the oven, the surface-to-volume ratio, and the time the wood is in the kiln. Then there’s the fact that we don’t know how they kiln-dried it. The exact process, the moisture content they’re aiming for, the temperature, the time, what kind of kiln they use... all that depends on what the wood is being used for. It could be anywhere from 140 to 240 degrees Fahrenheit (depending on species), in a high or low humidity environment, for virtually any extent of time. There is no set process as it is up to the manufacturer’s preferences, and what they want the wood to be used for.

Since bedding is often simply chipped-up waste wood from other industries, we have no way to determine what the drying standards were. Therefore, even if a bedding has been kiln-dried, we have no guarantees that it was done to remove a sufficient amount of VOCs from the wood... and remember, the process is focusing on removing water, not other compounds. We could say “the process removed 10 grams of phenols” BUT can we confirm how much is left? Not without analyzing the wood, the release rate of VOCs during the process... and thereby shifting the industry focus from water to the compounds. In the end, all we know is that there is a “kiln-dried wood” stamp on the package, but that bit doesn’t really help us at all. The best it does is change our statement that “it’s definitely not safe to use” to “there’s no guarantee it’s safe to use.”

What about the people who claim that pine or cedar doesn’t affect their hamsters?
Well, I can definitely promise that their hamsters aren’t special. They don’t have some amazing immune system that can fight off things that harm other hamsters. The best way I can explain is through an analogy. We all know that smoking is harmful, correct? Some people react immediately to it - asthma, reduced lung capacity, inflamed throat and lungs. But not everyone shows those symptoms, or some show them later on. BUT even though someone may not get asthma attacks from smoking, we still know that the smoke is damaging the cells in their lungs. In the same way, even if there are no visible reactions to the abietic or plicatic acid, we still know that some amounts are being inhaled. We still know that it will cause cell death - even in small amounts, it’s still happening - and that eventually the damage will build up. And we know from the studies cited above that once that damage occurs, there’s no guarantee of recovery, even after several years. Therefore, even if you can’t see symptoms from the damage, that damage is still occurring.


Some of those sources are old. Are they still worth reading?
The quick answer to that is YES. Just because a study is old does not make it invalid.
The in-depth answer is that it depends on what you’re looking for. For example, the fact that cedar contains plicatic acid has not changed in the years since it was discovered. The tree would have to evolve for that study to become invalid. Similarly, the fact that abietic acid is cytotoxic has not changed. It’s still going to damage cells regardless whether it’s 1980 or 2013. Now what can change are things like occupational studies. A study on woodworkers in 1974 can tell us that wood dust is a carcinogen because woodworkers were getting sinus cancer. BUT that doesn’t mean that today’s woodworkers get sinus cancer, because now we have OSHA and EPA standards for air quality and working environment. However, the wood dust is still dangerous, even if the woodworkers are now protected from it.

2. ~ From American Fancy Rat & Mouse Association



The Problem With Pine: A Discussion of Softwood Beddings

By Elizabeth R. TeSelle, Nashvile, TN


Most rat and mouse people know to avoid cedar shavings. The primary reasons for doing so have been the increased incidence of respiratory problems, including pneumonia, and suspected links to various forms of cancer. However, many people may not realize that not only are there additional dangers associated with cedar shavings, but that pine shavings contain similar toxins and consequently, can be linked to similar problems.


Many people may not realize that not only are there there additional dangers associated with cedar shavings,

but that pine shavings contain similar toxins.


Stories of long-lived rats and mice are, perhaps, apocryphal. However, several years ago, when discussing the cedar/pine issue with a veterinarian, I heard a particularly interesting tale. This man had lived with a number of rats over the years, and while most of them had used pine shavings as bedding, the rat he owned while he was in school (and very poor) lived primarily on shredded newsprint. Although every other rat he owned lived the standard 2–3 years, this particular rat lived (according to him) over 6 years. He remembered this rat as we talked about cedar and pine and wondered if perhaps there was a connection. While such a story does not constitute proof, it is food for thought.

Rabbits And Pine

In 1989, the House Rabbit Society, which has fostered thousands of rabbits until homes can be found for them, made an accidental discovery (Harriman 8-9). When a young, healthy rabbit died following a routine spay, HRS ran blood work and discovered that the rabbit’s liver enzymes were elevated far above normal. Because there was no obvious reason for this elevation, blood chemistries were run on rabbits in foster homes around California, many of whom turned up with the same enzymes elevated. The only difference noted in the rabbits’ environments was that those with elevated liver enzymes were all using pine shavings in their litter boxes or cage trays; the ones with normal livers were using cat litter.

In order to determine if the pine shavings were indeed at fault, the shavings were replaced with cat litter and the rabbits’ blood levels were rechecked a month later. Without exception, all the previously abnormal liver enzymes had returned to normal. At the same time, an informal survey was conducted of HRS members whose rabbits had died of liver disease (diagnosed upon autopsy or through blood work). Invariably, either cedar or pine shavings had been used with all of these rabbits.

As far as possible connections with rats and mice go, it is important to realize that without blood work, a liver biopsy, or an autopsy, it is difficult to diagnose liver disease. Consequently, while liver disease may not be documented as a common cause of rat and mouse deaths, many cases of rats and mice dying of “old age” may in fact have been related to liver failure. When an older rat or mouse stops eating, becomes lethargic, and just “fades away,” many causes are possible, but liver disease is certainly among them. It is true that rats and rabbits are different species, but in general, what is hepatotoxic (causative of liver damage) in one mammalian species is hepatotoxic in another. This is why rats and rabbits are used so often in pharmacological studies involving adverse drug reactions in human beings.

Phenol Alert

Although this information is hardly common knowledge, the laboratory animal community has recognized since at least 1967 that cedar and pine shavings, both of which contain phenols, are potentially toxic to small animals (Vesell, Cunliffe-Beamer). Phenols are caustic, poisonous, acidic compounds present in softwoods, which are routinely diluted for use in disinfectants (for instance, Pine-Sol and Lysol both use phenols and can cause liver and kidney damage in rodents, rabbits, cats, dogs, and humans). They are what make disinfectants cover smells and cedar and pine shavings cover the smell of animal urine.

Since phenols are caustic, their direct connection to respiratory problems and pneumonia in rats, mice, and guinea pigs is clear. The constant irritation to the nasal passages, throat, and lungs gives harmful bacteria an easy opening. Phenols also affect organs such as the liver and kidneys because these organs are responsible for filtering blood and urine and eliminating toxins from them. While the kidneys and liver can handle a small amount of toxins, when they are presented with a large amount over time, they are unable to filter it all out and begin to fail. In addition, a rat or mouse with a damaged liver will have a depressed immune system, which can lead to more common “old age” symptoms such as respiratory and pulmonary infections. Interestingly, one of the main causes of death in older hamsters is amyloidosis of the kidneys. The cause is often considered idiopathic (not known), but if cedar and pine shavings can damage the kidneys, the possibility for a connection between bedding and disease once again surfaces.


Phenols are caustic, poisonous, acidic compounds present in softwoods, which are routinely diluted for use in disinfectants.



Researchers Study Wood Beddings

One of the early medical studies of softwood beddings and hepatotoxicity found a connection between the use of red cedar, white pine, and ponderosa pine and changes in both barbituate sleep time and the activity of liver enzymes (Vesell 1057). The researchers proved that the length of barbituate sleep time (the amount of time a mouse or rat stays “out” when under a controlled dose of anesthesia) was inversely proportional to the level of enzyme activity in the liver (i.e., that sleep time decreased as enzyme activity increased). This inverse ratio occurs because the hepatic enzymes control the metabolism of the barbituates. In an attempt to deal with the toxin (phenols, in this case), the liver produces more enzymes and hence, wakes the mouse up sooner. This study determined that softwood beddings alter the liver’s activity in response to drugs significantly enough to suggest that such beddings not be used for animals in pharmacological experiments for fear of skewing the results.

Another study goes even further. It concludes that rats and mice kept on four bedding types were affected most by red cedar, but that white pine was the next most hepatotoxic bedding. In fact, “sleep times of C57BL/6J male mice on each bedding were significantly different in the following order: mixed hardwood > white spruce > white pine > red cedar. In both strains, liver:body ratios of mice on red cedar bedding were significantly increased compared to mice on white pine, white spruce, or mixed hardwood beddings” (Cunliffe-Beamer 672). Mice kept on mixed hardwood bedding slept an average of 135 minutes, while those on cedar slept an average of 56 minutes. Mice housed on white pine slept an average of 85 minutes—between the other two sleep times, but closer to the sleep time of cedar than that of hardwood (see Table 1). Enzyme activity was significantly increased in cedar and pine mice and their livers were heavier (i.e., more greatly damaged) than those mice kept on hardwood. It is important to realize that the level of hepatotoxicity noted here was induced by only 24 hours to 5 days of exposure to the beddings in question.

Bedding                        Sleep time (minutes)
                                     (combined mean of

                                      autoclaved and unautoclaved bedding -

                                      C57BL/6J mouse strain)

Hardwood                     135 +/- 6

Spruce                          123 +/- 5

Pine                               85 +/- 4

Cedar                            56 +/- 3


TABLE 1. Adapted from Cunliffe-Beamer 673.

Other studies abound, including one concerning cocaine hepatoxocity in different species of mammals. In addition to studies with non-pretreated animals, the researchers intentionally induced liver damage in some of the mice solely by housing them on pine shavings! (Connors) Another study determined that exposure to both hardwood and softwood dust can cause squamous cell cancers of the upper respiratory tract (Vaughan).

Clearly, there is sufficient evidence to suggest that pine shavings can cause similar problems to cedar shavings, and that therefore, they should be avoided. Because none of these studies included a non-wood bedding in their samples, it is difficult to know if hardwood bedding is truly safe, but hardwood beddings, or the softwood spruce, which in the 1981 study appears to be less toxic than cedar and pine, are certainly safer choices.

Wood Alternatives

There are many alternatives to wood shavings, most of which are just as absorbent and make excellent bedding. Perhaps the nicest of all is CareFRESH™, a paper pulp product which is made from non-toxic, untreated cellulose fiber. The pieces are small and soft (not pelleted), and in fact feel very much like shavings. CareFRESH™ is truly dust-free, controls odor beautifully, and makes a nice nest. Another option is plain, unprinted newsprint. Most newspapers will either give away or sell for a nominal cost the end of their newsprint rolls, which can then be shredded into comfortable, absorbent bedding and used in sheets on the bottom of the cage.


Many cases of rats and mice dying of “old age” may in fact have been related to liver failure.


The dangers posed by pine shavings are just as serious as those posed by cedar. While cedar shavings may smell stronger, all softwoods contain deadly phenols, and pine has been implicated in organ damage and respiratory disease just as cedar has. While in the past this information was not widely disseminated, there is now sufficient evidence that softwood beddings are just not safe for small animals. Please consider discontinuing their use—and let’s all try to educate pet stores and veterinarians as well. 



NOTE: The medical articles referenced here should be available through inter-library loan at your local library. Each article also contains references to other studies in this area.


bottom of page