A runny nose is almost always irritated nasal tissue making extra mucus, most often from a common cold or from allergies.
The pattern tells you a lot. Cold viruses start with a scratchy throat, then thin drainage that thickens over a few days and settles within about 7 to 10 days. Allergies bring clear, watery drainage with sneezing and itchy, watery eyes, and they follow exposure to pollen, dust mites, or pets rather than a fixed timeline. Cold air, exercise, crying, and spicy food can also set off a short drip that stops on its own. Saline rinses, steam, fluids, and removing the trigger handle most cases at home.
How to stop a runny nose
Common questions
why is my nose runny
A runny nose comes from swollen nasal tissue producing extra mucus. Viral colds are the most common cause and usually clear within 7 to 10 days. Allergies cause thin, clear drainage with sneezing and itchy eyes, and they track with exposure rather than a set timeline. Cold air, spicy food, and strong odors can trigger a brief drip. Thick colored mucus that lasts past 10 days, or improves and then worsens with facial pain and fever, suggests a sinus infection. See a clinician for drainage from one nostril only, clear fluid after a head injury, high fever, or symptoms that block your sleep and daily activity.