Thank you for getting back to me. I would get rid of the pine bedding at once. For a long time, we knew cedar shavings caused problems, but we've now learned that pine does, too. It gives off volatile oils that irritate the skin and respiratory systems. It could cause sneezing. CareFresh brand, in the unscented and uncolored varieties is the least likely to cause irritations. The first thing I would try is a switch to CareFresh. I also recommend that you get rid of the fluff bedding for another reason. Hamsters do love it and it provides a soft bed, but they carry their bedding around in their pouches, and fluff bedding tends to stick in the pouches. That leads to a cheek pouch impaction, which must be treated by a vet. I'm glad to hear that you don't use anything with artificial fragrance or any spray cleaners. Both can lead to all sorts of health problems.
The three most common causes of sneezing without any other symptoms are irritations, allergies, and foreign bodies in the nose. If you eliminate all bedding except CareFresh, and the sneezing continues, there is probably something stuck in your hamster's nose. Because a hamster is so small, it doesn't take much - a bit of bedding, a tiny seed, etc. If that turns out to be the problem, you will need to see a vet to have it removed. Many vets are not experienced with small rodents, and it would be best to find one who is. If you end up needing to see a vet, here is a link to a directory of rat vets (who will also be good with hamsters):
If you have more questions, just let me know by clicking on REPLY. I hope the bedding change will solve the problem.