Urine – including cat urine – contains a substance called urea. It doesn’t smell much but if you let it sit for a while, bacteria will start to break down the urea into ammonia, which releases the ammonia odor.
Typically, you won’t notice this smell because the litter will cover it. However, in some cases, the smell can be more pungent than usual. The stinky odor can occur when your cat is dehydrated or in case she has an inadequate diet. Also, it can be indicative of health concerns including infections and illness.
Whatever reason it may be, it’s important to take steps to minimize the smell and the harm or disruption it causes. To keep the ammonia smell at bay, try to clean the litter box as regularly as possible and ensure that your cat has plenty to drink.