What is the reason for a runny nose without symptoms?

Patient's question:

Always been flowing, and it's clear mucus, with no other symptoms
Past treatment history and effectiveness: None
Regardless of what kind of assistance: What caused it, how to treat it

Doctor's answer:

It is important to maintain fresh indoor air at all times. Frequently open windows for ventilation and air exchange, at least twice a day for 20 minutes each time. This can help reduce the risk of respiratory infections. The indoor temperature and humidity should be comfortable, with a room temperature of about 22-25 degrees Celsius and a humidity of 50%-60%. Lastly, let the child stay away from public places as much as possible, especially during periods of prevalent fever. Avoid taking children to crowded public places such as shopping malls or convenience stores, and do not visit sick people to prevent cross-infection. It is usually a case of catching a cold, so pay attention to staying warm.