Humidifiers are not designed to make you sick but primarily used to make you healthy. If you don’t clean your humidifier regularly (about every 3 days) it can breed dirt and microorganisms that can give you flu-like symptoms. If your humidifier has a filter you should consider changing it around every 3 months to prevent dirt and bacteria being released into the air. Be sure to replace the water often to help prevent bacteria from growing that could make you sick.