Runny nose is excess drainage, which may range from a clear fluid to thick mucus, produced by the nasal and adjacent tissues and blood vessels in the nose. The drainage of runny nose may run out of your nose or down the back of your throat or both.

The terms "rhinorrhea" and "rhinitis" are often used interchangeably to refer to a runny nose. Strictly speaking, rhinorrhea refers to a thin, relatively clear nasal discharge. Rhinitis refers to inflammation of the nasal tissues from a number of causes, which usually results in a runny nose.

Nasal congestion may or may not accompany runny nose.

Less commonly, runny nose can be caused by polyps, a foreign body, a tumor or migraine-like headaches.

Causes of runny nose include:

1. Acute sinusitis
2. Bright lights
3. Chronic sinusitis
4. Churg-Strauss syndrome
5. Cluster headache
6. Cold temperature
7. Common cold
8. Decongestant nasal spray overuse
9. Deviated septum
10. Drug addiction
11. Dry air
12. Dust mite allergy
13. Food allergy
14. Hay fever
15. Hormonal changes
16. Influenza (flu)
17. Latex allergy
18. Lodged object
19. Medications
20. Milk allergy
21. Mold allergy
22. Nasal polyps
23. Nonallergic rhinitis
24. Occupational asthma
25. Other infections
26. Peanut allergy
27. Perfume
28. Pet allergy
29. Pregnancy
30. Respiratory syncytial virus (RSV)
31. Shellfish allergy
32. Soy allergy
33. Spicy foods
34. Spinal fluid leak
35. Tobacco smoke
36. Wegener's granulomatosis
37. Wheat allergy

Causes shown here are commonly associated with this symptom. Work with your doctor or other health care professional for an accurate diagnosis.

Source: mayoclinic.org

Call your doctor if:

• Your symptoms last more than 10 days.
• You have a high fever, particularly if it lasts more than three days.
• Your nasal discharge is green and is accompanied by sinus pain or fever. This may be a sign of a bacterial infection.
• You have asthma or emphysema, or you're taking immune-suppressing medications.
• You have blood in your nasal discharge or a persistent clear discharge after a head injury.

Call your child's doctor if:

• 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.

Self-care
Until you see your doctor, try these simple steps to relieve symptoms:

• Sniffing and swallowing or gently blowing your nose.
• If the runny nose is a persistent, watery discharge, particularly if accompanied by sneezing and itchy or watery eyes, your symptoms may be allergy-related and an over-the-counter antihistamine may help. Be sure to follow the label instructions exactly.
• For babies and small children, use a soft rubber suction bulb to gently remove any secretions.

Try these measures to relieve postnasal drip — when excess mucus accumulates in the back of your throat:

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

Source: mayoclinic.org