[AmityvilleHams]

Aspen can definitely cause an allergic reaction. While it may not be the sole factor for your hamster's issues it could contribute. A lot of people don't think about that but it's hardly unheard of!

For this cotton n card bedding, I would say don't use it. Cotton has at best questionable safety, and we already know the serious dangers it poses in other forms. Even if it doesn't seem like the obviously dangerous fluffy stuff taking that risk is a very bad idea!

Carefresh in general is a very poor choice. It's a highly processed pulp often with added dyes - and an unknown odor control formula when I last checked which has questionable at best safety. We've seen many hamsters react negatively to Carefresh due to the high dust levels alone, and with it being a lesser known fact that Carefresh does source some fiber from toxic wood species that should also be a significant concern.

With aspen potentially triggering a reaction in this hamster I wouldn't be using wood substrate in general including Chipsi. It is possible that some wood species may not trigger these same reactions, but I wouldn't want to take that risk introducing more wood species that are even more likely to cause a reaction.

I would personally try hemp. It wouldn't be hard to find in the Netherlands(just make sure there are no additives as some companies do add unsafe things to hemp), and it is very unlikely that a negative reaction to hemp would occur. Typically we see hemp allergies in humans here rather than hamsters - and even that isn't overwhelmingly common!