Hamsters can catch cold and flu from humans, so if you're suffering from one, try not to handle your pet to avoid the spreading of your virus. Hamsters can also catch a cold from being in a draught.
Sneezing and a runny nose are typical symptoms of a cold, in more severe cases your hamster may have runny eyes, weightloss, wheeziness and lethargy.
If your hamster is only showing mild symptoms keep them warm (not too hot) and away from a draught. If the symptoms don't clear up within a few days or get more serious seek medical attention from your vet.