Causes of a runny nose include:

• Acute sinusitis
• Allergies
• Chronic sinusitis
• Common cold
• Decongestant nasal spray overuse
• Deviated septum
• Dry or cold air
• EGPA (formerly Churg-Strauss syndrome)
• Granulomatosis with polyangiitis (a condition that causes inflammation of the blood vessels)
• Hormonal changes
• Influenza (flu)
• Object in the nose
• Medicines, such as those used to treat high blood pressure, erectile dysfunction, depression, seizures and other conditions
• Nasal polyps
• Nonallergic rhinitis
• Pregnancy
• Respiratory syncytial virus (RSV)
• Tobacco smoke

A runny nose is having fluid run out of the nose. The fluid can range from thin and clear to thick and yellow-green. The fluid might drip or run out of the nose, down the back of the throat, or both. If it runs down the back of the throat, it's called postnasal drip.

A runny nose is often called rhinorrhea or rhinitis. But the terms are different. Rhinorrhea involves a thin, mostly clear fluid running from the nose. Rhinitis involves irritation and swelling inside the nose.

Rhinitis is the usual cause of a runny nose. A runny nose also might be stuffy, also called congested.

Anything that irritates the inside of the nose can cause a runny nose. Infections — such as colds, flu or sinusitis — and allergies often cause runny and stuffy noses. Some people have noses that run all the time without a known reason. This is called nonallergic rhinitis or vasomotor rhinitis.

A polyp, an object such as a small toy stuck in the nose, or a tumor might cause the nose to run from only one side. Sometimes migraine-like headaches can cause a runny nose.

• Your symptoms last more than 10 days.
• You have a high fever.
• What comes from your nose is yellow and green. Your face hurts or you have fever. This may be a sign of a bacterial infection.
• What comes out of your nose is bloody. Or your nose keeps running after a head injury.

• Your child is younger than 2 months and is running a fever.
• Your baby's runny nose or congestion causes trouble nursing or makes breathing difficult.

Until you see your health care provider, try these simple steps to relieve symptoms:

• Avoid anything you know you're allergic to.
• Try an allergy medicine you can get without a prescription. If you're also sneezing and your eyes are itching or watering, you might have allergies. Be sure to follow the label instructions exactly.
• For babies, put several saline drops into one nostril. Then gently suction that nostril with a soft rubber-bulb syringe.

To relieve saliva that builds up at the back of the throat, also known as postnasal drip, try these measures:

• Avoid common irritants such as cigarette smoke and sudden humidity changes
• Drink plenty of water.
• Use nasal saline sprays or rinses.