Certain items are harmful and so should never be used as bedding for your hamster.
Pine and cedar wood shavings can cause respiratory infections so should not be used as floor covering, although pine can be safer if it is kiln dried. Scented wood shavings are also unsafe, while corn cob bedding should be avoided as it can sometimes start to mold and can swell in the stomach if eaten. Sawdust is unsuitable as it can cause irritation to your hamster’s eyes.
For nesting material, any fluffy types of bedding should be avoided as they can become stuck in cheek pouches and your hamster can potentially get caught in the fibers. Furthermore, wool and pieces of material do not dissolve easily and can cause blockages if eaten. Straw is unsuitable as well since its sharp edges can cause injury.