Most rats you get from pet stores have a common type of chest cold. They just do. Not much can be done about it - it just rips through pet store populations and they have it for life. Also, double rex rats have whiskers that curl in towards thier nose and mouth - and they often sneeze a lot because of that. If this is a new addition to your home, you just need to be extra diligent about cleaning for the next little while and it should improve - although probably never go away entirely.
If you are using wood shavings as bedding - stop. Aspen is the only type of wood bedding rats aren’t allergic too and even many rats are sensitive to it. The fibre based stuff is more expensive, but many rats simply need it to be healthy.
If this is a new sneeze in an older rat - take it to the vet. If this rat’s teeth are getting long and you don’t know how to trim them properly - take it to a vet. [ Razhie's advice column | Ask Razhie A Question ]
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