Unscented cat litters are specifically designed to trap ammonia-based odors through their absorbent properties. These same products tend to be more environmentally-friendly as they don’t require additional chemicals to eliminate the strong odors produced from cat excretion. In addition, they’re safer for pregnant women for the same reasons.
Many cats don't like the strange smell in their litter. They just have a natural, raw bentonite smell. So we don't necessarily have to add spices.