Yes, it is safe to sleep with a humidifier on all night. Humidifiers are designed to be used in sleeping environments and can reduce the risk of symptoms from colds, allergies, asthma and other respiratory conditions. When using a humidifier at night, make sure you keep an eye on the humidity levels in your room; this will ensure that they remain within optimal ranges for comfort and health. Additionally, take extra precautions by cleaning your humidifier regularly to avoid bacteria buildup which could lead to inhaling unhealthy particles while you're asleep. Finally, use only distilled water rather than tap water as it has fewer impurities that could be released into the air when heated up by your device.