Ammonia can be extremely harmful to humans. The severity of symptoms associated with ammonia exposure depends on the level of concentration and the length of time exposed to this gas. Contact can lead to burning of the nose, throat, lungs, and eyes, as well as nausea and other painful effects. One type of exposure comes from household ammonia, often created by mixing different cleaning products. This is something that you should never do. 

Prolonged or intense exposure can result in long-term side effects, including blindness, chronic coughing, and even death. The best course of action after ammonia exposure is to get fresh air by opening windows and doors or even leaving the building. If getting outside is not possible, lie low as ammonia is lighter than air and will rise. In case of an emergency, call poison control immediately.