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Just about everyone has experienced a runny nose at some point. This symptom can have many different causes and characteristics.

For example, a runny nose may only last a short time in some people and may be constant in others. The color of the nasal discharge can vary as well.

In some cases, you may have a runny nose with clear fluid that’s constant or persistent.

Below, we’ll explore some of the causes of a constant runny nose with clear fluid. We’ll also address what you can do to ease your symptoms, and signs that it may be time to see your doctor.

A runny nose happens due to an increase in the production of nasal mucus. While a runny nose can have many causes, it often occurs due to inflammation of the tissues inside your nose. This is known as rhinitis.

The extra fluid that’s produced can drain from your nose, down the back of your throat (postnasal drip), or both. While nasal mucus can have a variety of colors, the medical term for a runny nose with thin, clear fluid is rhinorrhea.

Now let’s examine some of the potential causes of a constant runny nose with clear fluid.

Allergies are a common cause of a constant runny nose. When allergies affect your nose, it’s called allergic rhinitis or hay fever.

With allergic rhinitis, your immune system overreacts to something that’s typically harmless, such as pollen, mold, or pet dander. This leads to inflammation in your nasal passages and increased mucus production.

Nasal discharge due to allergic rhinitis is often thin, watery, and clear. It may last as long as a particular allergy trigger, called an allergen, is present in your environment.

In addition to a runny nose, some other symptoms of allergic rhinitis include:

Non-allergic rhinitis is a term that describes nasal symptoms that develop in the absence of allergies or an infection. It’s believed that this condition may happen when blood flow in your nose increases. This can lead to swelling and an increase in mucus production.

While the exact biological cause of non-allergic rhinitis is unknown, a variety of factors can trigger it, including:

  • Foods: Symptoms can develop any time you eat, but may be more likely when you consume food that’s spicy or has a hot temperature. Alcohol can also trigger symptoms.
  • Medications: Taking some types of medications can lead to non-allergic rhinitis symptoms. Some examples include:
  • Irritants: Some examples of irritants that may trigger non-allergic rhinitis include:
    • cigarette smoke
    • pollution
    • dust
    • chemical fumes
    • perfumes
  • Changes in weather: Changes in temperature or humidity may trigger symptoms of non-allergic rhinitis.
  • Hormone fluctuations: Changes in hormones due to things like pregnancy, menstruation, and hypothyroidism can cause non-allergic rhinitis.
  • Stress: An increase in stress levels can also lead to non-allergic rhinitis symptoms.

The symptoms of non-allergic rhinitis can include a runny nose, with discharge that’s thin, clear, and watery. Other symptoms may include:

  • nasal congestion
  • postnasal drip
  • sneezing
  • coughing

Non-allergic rhinitis is a chronic (long-lasting) condition. Its symptoms can be persistent, happen on and off, or occur at specific times of the year.

Treatment for non-allergic rhinitis is focused on using medications to relieve symptoms when they’re present.

Viral infections like the common cold and the flu attack the tissues of your nose and throat. In response, your nose produces more mucus to help trap and wash viral particles away. This can cause a persistent runny nose with clear fluid.

In addition to a runny nose, some of the common symptoms of a respiratory virus infection include:

It’s important to note that the presence and frequency of some symptoms can depend on the virus that’s causing the infection. For example, a runny nose happens more often with the common cold than with the flu.

A runny nose due to the common cold can last from 10 to 14 days. Most flu symptoms will go away in 3 to 7 days, although fatigue and cough may linger for two weeks or longer.

Some pregnant women may experience a runny nose that occurs without a previous history of infection, allergies, or other nasal conditions. In addition to runny nose, other symptoms can include nasal congestion and sneezing.

It’s believed that changes in hormones, such as estrogen and progesterone, can cause pregnancy rhinitis. These changes can lead to increased blood flow in the nose, resulting in inflammation and excess mucus.

Although the symptoms of pregnancy rhinitis can start at any point during pregnancy, they’re more frequently reported during the third trimester. Symptoms typically disappear shortly after delivery.

Nasal polyps are benign (non-cancerous) growths that develop in your nasal passages. They result from chronic inflammation in this area and are associated with other conditions, such as allergies and asthma.

The chronic inflammation associated with nasal polyps can lead to symptoms like a persistent runny nose.

Some additional symptoms of nasal polyps may include:

Over-the-counter (OTC) and prescription medications can be used to shrink or get rid of nasal polyps. These medications can ease symptoms, including runny nose. However, if drugs aren’t effective, surgery may be needed to remove them.

Nasal foreign bodies are more common in children than adults. This happens when an object is stuck in the nose that shouldn’t be there. Some examples of common nasal foreign bodies, especially with young children, include beads, pebbles, and rubber erasers.

The presence of a foreign body can irritate the tissues of your nose, leading to inflammation. This can cause a persistent runny nose that:

  • typically occurs on the side in which the foreign body is stuck
  • can sometimes be clear in color, but may also contain pus or blood
  • is often foul-smelling

Other symptoms that can occur are:

  • a feeling that your nose is blocked
  • sneezing
  • headache

A doctor can help remove a foreign body that’s become lodged in the nose. Symptoms should begin to clear once the foreign body has been removed.

Cerebrospinal fluid (CSF) is a clear liquid that’s found in your brain and spinal cord. It helps keep these areas healthy by giving them protection, providing nutrients, and removing waste products.

In rare cases, CSF may leak out of the brain. This can happen due to a head injury or surgery. A CSF leak can also happen spontaneously. This is a serious health condition that requires immediate medical evaluation.

If you have a CSF leak, you may experience clear fluid draining from your nose or ears. Other symptoms include:

It’s possible that a CSF leak will resolve on its own. However, surgery is often needed to address the condition. People with a CSF leak are at an increased risk of developing meningitis.

There are several things you can try at home to help clear up a runny nose.

While a runny nose will often go away with at-home care, there are some signs that it may be time to make an appointment with your doctor. These include:

  • a runny nose that doesn’t clear up after 10 days
  • high fever
  • symptoms of a bacterial infection, such as fever and mucus that’s become yellow or green in color
  • bloody nasal discharge
  • clear nasal discharge that happens following a head injury

There are many possible health conditions that can cause a constant, clear runny nose. Some of the most common causes include allergies, infections, and nasal polyps.

Some other factors that can trigger a constant, clear runny nose include food, medications, and changes in hormones.

Most causes of a constant clear runny nose can be treated with OTC medications and home remedies. See your doctor if your symptoms last longer than 10 days or if you also have other symptoms, like a high fever or bloody nasal discharge.