What health effects can be caused from breathing human urine?

Breathing animal urine does not pose a risk to most people. However, in concentrated amounts found in poorly ventilated areas, ammonia fumes produced by animal urine can cause a number of serious symptoms after long-term exposure. These symptoms may include burning and watering of the eyes, coughing, wheezing, headache, and nausea, among others. The World Health Organization considers ammonia to be a possible carcinogen, meaning that inhalation of these fumes may be linked to cancer growth. Never clean up animal urine that has a strong ammonia smell with bleach; mixing bleach with ammonia will cause toxic gases to form.The most common symptoms reported include headaches and burning, watery eyes.