How can breathing cat urine affect you?

Exposure to cat feces can cause the disease toxoplasmosis, but this disease is extremely, extremely rare among indoors-only cats. So there is no need to worry about toxoplasmosis if your cats are indoors-only cats.

Cat urine is not harmful to your health. It contains ammonia, and ammonia fumes are very harsh and noxious. People think that since it has such an overpowering smell, it must be harmful to your health, but this is an erroneous assumption.

Many cat litters, especially the classic clay kind, are filled with harmful toxins. When you pour the fresh litter into the box, or dig around in it vigorously, or the cat digs around, some of it breaks up and floats up into the air, and you inhale it. So you want to avoid breathing it in as much as possible. Using a covered litter box is also a good idea.

But obviously, the problem is not the urine or feces, but the litter. And you don't HAVE to use clay litter. They are many, many different types, like the crystal kind (which may not be less harmful, but is much less dusty). There are even "organic" brands made with all-natural ingredients.