Clear fluid leaking from the nose can result from a variety of different inflammatory causes, including allergies and a sinus infection. It's also a symptom of cerebrospinal fluid (CSF) rhinorrhea, but it's different from a typical runny nose because it causes continuous dripping out of one nostril. This rare condition happens when fluid surrounding the brain leaks through the nose.

Most often, a runny nose is caused by allergies, the common cold, or cold weather. CSF rhinorrhea can be caused by an injury or a surgical complication.

This article discusses the causes, symptoms, and treatment of CSF rhinorrhea. It also explains how you can tell the difference between a common runny nose and a CSF leak.

Symptoms associated with a runny nose are familiar and include:

While there is some overlap with symptoms of a CSF leak, this type of rhinorrhea can also cause more unusual symptoms.

Symptoms of a CSF leak can include:

You may be able to tell if you have a CSF leak by the way your nose is draining.

Nasal discharge can be thick or thin, colored, or clear

Nasal discharge comes out of both nostrils

Usually improves with cold or allergy medications

Does not typically cause loss of smell

Nasal discharge is thin and clear

Nasal discharge may come out of only one nostril

Does not improve with cold or allergy medications

Can cause loss of smell

The brain and spine are surrounded by cerebrospinal fluid. This fluid is contained by connective tissue called the dura mater.

When there is a tear or hole in the dura mater of the brain, it is known as a cranial CSF leak. This causes CSF to leak into the sinuses (two sets of cavities in your head) and out through the nose. This is different from a spinal CSF leak, in which the fluid leaks from the spine and does not cause nasal symptoms.

Causes of CSF rhinorrhea include:

With CSF rhinorrhea, bacteria can spread from within the nasal passages and sinuses through the hole in the dura and into the lining around the brain.

This can cause bacterial meningitis, a life-threatening infection.

If you're experiencing a runny nose without other allergy symptoms, or a runny nose that doesn't get better with time or with allergy medication, ask your healthcare provider if you should be evaluated for a CSF leak. This is especially important if you had a head injury before a runny nose started or if you have ever contracted meningitis.

While CSF rhinorrhea is a rare condition, if you have a chronic runny nose without other symptoms of nasal allergies (allergic rhinitis), such as sneezing, nasal congestion, and watery eyes, you may need to be evaluated for the condition.

Anyone who has had repeated episodes of bacterial meningitis should also be evaluated.

Tests used to diagnose a CSF leak include:

Often, a CSF leak will heal on its own with bed rest in a matter of days to a week. However, a CSF leak should always be evaluated due to the increased risk of meningitis.

If the leak does not respond to conservative treatment, it may need to be surgically corrected.

Most commonly, a CSF leak is fixed with a minimally invasive nasal endoscopy and will resolve within seven to 10 days.

A surgeon inserts a flexible tool with a light and camera into a nostril to see inside. While viewing the affected area on a monitor, they patch it using a graft. The graft can either be artificial tissue or a piece of your tissue or fat.

Cerebrospinal (CSF) rhinorrhea is a rare condition in which spinal fluid leaks from a tear in the meninges into the sinuses and nasal passages. CSF rhinorrhea is different from a runny nose caused by a cold or allergies. The fluid is always thin and clear, and symptoms don't improve with cold or allergy medicines.

Once a CSF leak is diagnosed, the leak may be left to heal on its own or a surgeon may perform a nasal endoscopy to repair the tear.