Ammonia in your cat's urine is the reason your nose would like to shut down and your eyes would like to seal shut when you walk by your cat's litter box when it's getting time to change it. The powerful stench isn't usually a cause for concern -- although, if you have respiratory problems, your lungs might disagree.
Ammonia -- a compound of nitrogen and hydrogen -- is caustic and hazardous, but ammonia buildup in your cat's litter box isn't deadly in most circumstances. If you have asthma or other respiratory problems, a slight ammonia scent can cause you to experience an adverse reaction, one such as coughing, tightening in the chest or, in the case of people with severe asthma, an asthma attack. If you let the cat's box go without changing for too many days, the scent might become strong enough to give you a headache and make your eyes water.
There's no replacement for daily litter box cleaning, even if you have only one cat. If you have multiple cats that use the same box, twice-daily cleaning may be necessary. Your cat will certainly appreciate it, too, although he's likely to ruin the box's sanitary state immediately after you scoop the litter. Running the bagged litter out to a sealed trashcan will prevent the nasty smell from wafting through the air. If you're leaving for a couple of days, ask whomever's taking care of your cat to scoop the litter while you're gone so you're not assaulted by the stench of ammonia when you return.
Placing your cat's litter box in the basement or in the laundry room, letting the washer and dryer deal with the occasional bad smell, is the best option. Litter boxes placed in open spaces rather than in tight areas will alleviate the possibility of fumes becoming hazardous.
If tossing out your cat's waste daily doesn't improve the smell around your cat's box, it may be time for new litter. That doesn't necessarily mean changing to a new brand. After each cleaning, the layer of clean litter diminishes. Eventually it reaches a point where it's not absorbing the smell of waste. Dumping out all of the litter after two weeks and replacing it with a new layer will remedy the problem.
If that doesn't work, trying a new brand can't hurt, unless your cat despises it. As long as you use the same type of stuff as your old cat litter -- in other words, replace nonscented with nonscented -- your cat probably won't care. If you do choose a new type or brand of cat litter, dust-free litter creates fewer health problems for your cat. According to the Cornell University College of Veterinary Medicine website, dusty cat litters may cause asthma in cats.