The ammonia smell that results from the urine in the cat litter can be toxic if the concentration is high enough. Among other things, prolonged exposure to the smell of ammonia from cat litter can cause coughing, nausea, irritated lung membranes, eye irritation and abnormally high heart rate. Certain bacteria that live in a cat's faeces can also be particularly damaging, although acquiring the bacteria through smell is somewhat unlikely.
Particular Hazards For Pregnant Women
Besides the ammonia smell coming from the cat urine, cat faeces can also be a danger. Faeces contain toxoplasmosis, a bacterium that can cause illness. If this disease is passed onto a pregnant woman, her baby may suffer from birth defects like mental retardation. The child being stillborn is the worst case scenario. Toxoplasmosis is a disease that can be spread from cats to humans. However, simply smelling cat urine coming from a litter box does not pose any greater danger to a pregnant woman.
Environmental Protection Agency
The EPA has classified ammonia as a toxic chemical and requires notification to a community when there is an abnormally high concentration of ammonia in the area. Ammonia is colourless, but has a truly distinct and foul odour at concentrations of 50 parts-per-million. Repeated exposure to ammonia, even of lesser concentration, can cause pneumonia, bronchitis, eye damage and skin cancer.
World Health Organization
The WHO has studied the effects of ammonia in both water and air. An airborne fume released by ammonia, in conjunction with the organic materials contained in cat litter, has been found to be dangerous in concentrations greater than 50 ppm. There is also some evidence that the interaction between ammonia and the bacteria which results in toxoplasmosis could potentially create a greater risk of harm, especially for children. In addition, some cat litter brands in both the U.S. and Europe contain the carcinogen crystalline, which could be potentially lethal when combined with ammonia.
Besides simply avoiding exposure to cat litter boxes, there are a few preventive measures to protect oneself from harmful exposure to cat litter fumes. The best way to prevent toxic fumes emitting from cat litter is to change the litter regularly, and to use a ventilated mask while doing so. To prevent against and carcinogenic complications, it is best to get cat litter that does not contain crystalline. Also, it is smart to keep cat litter boxes in a well-ventilated area.