To indicate stress, a hamster alternates between running and grooming as well as squeaking, biting and overeating. He also becomes more irritable, is more likely to bite, and may confine himself or hide. Over time as stress damages the digestive system, he can start to suffer from diarrhea or constipation.
A hamster can be easily stressed by changes in his environment. Routine tasks like cleaning his cage or handling him can upset and traumatize him, especially if he has just been moved and is not used to his new surroundings. To minimize stress, an owner should avoid waking a hamster up during the day and, if keeping multiple hamsters, ensure they are not behaving aggressively towards each other. A hamster remains stimulated by providing a running wheel, tunnels, toys and other entertainments. The cage needs to be large enough for the hamster to feel comfortable; if it is too small, a hamster may start gnawing on the bars. Finally, owners should make sure that the cage is placed in a temperate area that is not exposed to drafts or direct sunlight.
When a hamster is stressed, he also becomes more susceptible to disease and illness. For example, a recently weaned and agitated hamster is more likely to develop wet tail, a highly contagious disease that can result in death.