Aspen shavings and Carefresh bedding are recommended to be the safest, best types of bedding used. They are both a little more expensive than pine or cedar, but pine and cedar (especially cedar) have been reported as being toxic to small animals. They are both odorless, soft, and Carefresh especially is really good for absorbing odors. I personally use pine bedding because I can't get the other two types very readily in my area. I have never had a problem with pine. My hamsters all live to a ripe old age, with no serious health problems. Something else that helps is to make sure to keep the bedding cleaned frequently to cut down on any toxins that may be present. I would recommend reading the articles listed below and using your own judgement on what type is best for you.
Please avoid Cedar. If you would like more information about the danger of using Cedar or Pine, please take a look at these articles:
Litter & Liver Disease
The Toxicity of Pine and Cedar Shavings
Warning About Pine & Cedar Bedding
Some of this information is not specifically about hamsters, but it applies to all small animals. Most people are drawn to use cedar because of it's strong smell (to cover up odors) and because it is so cheap, but most people don't know the harm it can cause to their small animals either.
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