Hamsters are adorable small pets, and many families turn to them as the first pet for a child. While they do sleep the day away, they are very active at night. In their natural habitats, they would have miles and miles of territory to burrow and tunnel, and run. As a pet, it's the job of the pet parents to provide ways for their small animal friend to get ample exercise. Many turn to a wheel or an exercise ball for playtime outside of cages or make it a great temporary area to keep the little critter while you are cleaning their cage.  Perhaps not.
Hamsters are prey animals. If they find themselves in a large, open area, their natural instinct is to run away and hide. In a hamster ball, they can't do that. Without "protection," it can cause stress and fleeing behavior. If your hamster is running speedily in their ball, it may be a sign of stress and "escaping" behavior, not actually having fun. The ball also takes their sensory input away - they can't use their whiskers or paws to navigate their surroundings, the colored plastic distorts their vision, and they can't quickly come to a stop or change directions. In short, hamster balls can be a very stressful and disorienting experience for your furry friend.
As a pet owner, you can help your hamster become comfortable in an exercise ball. Most hamster balls are designed to split in half. Put half of the ball in your pet's cage, with a treat or two inside. After a few weeks, put together the exercise ball but leave the lid off. Let your hamster move in and out of the ball as it wishes. Let him get used to the plastic underfoot, to the color. Then, again after a few weeks, close the lid and monitor your pet. This monitoring is key. While hamster balls can seem like a great temporary holding area for your pet, you really shouldn't leave hamsters in them for longer than 10 to 15 minutes and never unattended. Watch to make sure they are active and alert and seem to want to run. Do they seem scared? Are they breathing quickly and seeming panicked? Does he simply seem uninterested and tired? Remember, not even humans feel like running at every given moment!
Hamsters can get their ball stuck in-between places as they try to run for a dark and narrow space. Being unable to free themselves can cause them to panic.  An improperly sized hamster ball will force your hamster to arch its backs while running, causing significant spinal problems and back pain. They could roll off steps or downstairs, resulting in sprains, trauma, fractures, internal injuries, and even death.
 The minimum wheel size for dwarf hamsters is 21cm and 25 - 30cm for larger Syrian hamsters.  It may take some extra searching and special ordering on your part, but you need to find an exercise ball that is the proper size for your little critter.  They may look ridiculous in a ball that large, but it's better than causing harm to your pet.
You should also set up a controlled exercise environment. Stairs and steps should be cordoned off with baby gates, for example. Children and other pets should stay out of the area - one accidental kick will send the ball zooming and your hamster turning head over hills. As much as possible, keep your hamster on a carpeted floor. This lets them control their direction better, as the carpet provides some resistance. On a hard floor, the ball rolls even after your small pet has stopped running.
The ventilation slits on most exercise balls are very small and can stress the hamster inside. This is likely intended to keep hamsters from getting their feet twisted, but the result is that ventilation inside the ball is poor. The dark translucent colors balls will absorb more heat and increase the temperature inside. Hamsters will sometimes urinate and defecate while inside an exercise ball, possibly as a stress response. However, they have no choice but to stay in the ball and run over their feces and urine. This can cause bacterial infections and ammonia burns on your pet's skin. The urine and feces odors also become trapped inside the ball. Darker colors of the translucent plastic will absorb heat, causing the interior of the ball to increase. Without the ability to get out on its own or access to water, your hamster could become overheated or dehydrated.
Hamsters should never be left in an exercise ball for so long that a buildup of fumes and heat would cause an issue - remember, 15 minutes tops, and monitored all the time. However, yes, hamsters will urinate and defecate in exercise balls. After each romp in the ball, take it apart and thoroughly clean it with soap and water. Clear hamster balls may get slightly discolored and scuffed from use, but they are also much less likely to trap heat. Always opt for a clear or otherwise light-colored hamster ball and make sure it has good ventilation.
If you have other pets or young children at home, they could play roughly with the hamster inside the ball and cause stress, injure or even harm your hamster. This could be a major problem if you have a cat or even young children at home. They could roll the ball down the stairs, play too roughly, or even open the top and cause your hamster to escape.
If you have small children or other pets at home, you must keep an eye on all parties during playtime to ensure the safety of these little animals.
Some pet owners are very opposed to the use of hamster balls. Others find that their pet hamster enjoys them. The key is to use them in a secure and safe way. Hamster balls provide interactive fun, healthy exercise, and a chance to explore surroundings in a free way. These are all good things! Just keep in mind a few added safety measures, and you can enjoy watching your little critter roll about your house.