Humidifier
It looks harmless enough. All it does is put moisture into the air to help you breathe better. But it could hurt your breathing, too. That’s because a fungus can grow in your humidifier and get blown into the air. The same problem might also happen in air conditioners and heating systems. Your lungs develop an allergy to the fungus and get inflamed. To avoid trouble, clean and service your heating and cooling system.