I'm off looking .................

. I don't have a bag at the moment but I don't think it says on the bag. One of the pet store descriptions says it's "paper based". Whatever that means. I did a lot of research into how cellulose was made some years back, when wanting to know what Carefresh was made of, and because it didn't feel like paper. At the time Kaytee was also cellulose but softer and stringier - but Kaytee changed the structure a few years ago.
My research showed that cellulose is made from wood pulp that has been through more processes - eg recycled paper and wood repulped. Whereas paper is made from tree wood pulp and goes through less processes. I found the info a long time ago and will see if I can find it again. It was in trying to work out how some pets can (apparently) be allergic to Carefresh and I could only think it was chemical residue from the extra processes. But that is just a guess. Whereas paper is hypoallergenic.
However both Kaytee and Carefresh are safe beddings (as you know!) It's just whether or not they could be hypoallergenic. If Kaytee C&C says it's "paper based" it sounds like it is probably a mix of recycled paper and recycled other pulp - but it does seem better quality than Carefresh. I've never heard of anyone having a hamster allergic to C&C.
But if a hamster had a suspected allergy, for process of elimination I would try paper bedding first, if it was me! If that makes no difference, then it's not bedding causing the allergy. While humans might react differently (I have skin allergies) - it can take 2 to 3 weeks for an allergy rash to disappear once the allergen is removed. And sometimes needs steroids to heal it up before it improves. Whether that's the same for hamsters I don't know, but I wouldn't expect it would disappear overnight!
I guess if you try hypoallergenic bedding for a few weeks and no difference, then try no sand for a few weeks and no difference - then it's not those - it's something else. I guess it could even be a food allergy.
I did read something recently that said Robos are not good with a lot of grain based and wheat based mixes like other hamsters - due to them not having so much of that in the wild - more seeds and insects. Whether that's true or not I have no idea. But wheat is one of the most common food allergens in humans.