Kitty litter is practically a staple for any cat owner, right alongside bread, butter and milk. There are no set ingredient list or "recipe" for commercial cat litter, although most varieties contain several common substances that increase absorbency, mask odors and allow the litter to clump more efficiently.
Clay containing sodium bentonite is one of the primary ingredients in most commercial cat litters. Bentonite clay can absorb about as much moisture as its original mass. Some organizations and individuals have voiced concern over the potential health hazard that this substance poses to humans as well as cats and other pets, although little definitive proof has been offered. Sodium bentonite itself is toxic and is linked to animal deaths, according to the Greyhound Companions of New Mexico.
Most manufactured cat litters contain silica, which is present in large quantities in natural sand and other mineral formations. While silica is not meant to be ingested, it is an inert substance; small quantities of it are relatively harmless to pets, according to the ASPCA. Silica is added as a gel or powder to increase the potential moisture absorbency of the litter mixture. Be aware that you can inhale powdered silica easily while cleaning or moving a litter box — it is the main component of the cloud of dust that rises from the litter box when it is disturbed. Inhaling enough of the dust can cause some respiratory distress, but is not confirmed to cause serious health problems.
Some commercial litter brands also include baking soda, although this ingredient is not as common as silica or bentonite clay. Baking soda is primarily an odor suppressant, so its use is primarily one of convenience rather than necessity. You can add baking soda to litter manually by sprinkling it directly on the litter. This is a good way to reduce odor problems if your cat isn't very diligent about burying his business when he's finished.
Alternative Cat Litter
Of course, not all kitty litter contains the aforementioned common ingredients. In fact, natural and organic litters may contain none of them at all. Sand, gravel and dirt can all function as cat litter without other additives, and some owners prefer these substances over commercial brands. Shredded paper, wood pulp and even whole corn kernels are organic, biodegradable alternatives to other varieties.