Your nose runs with a cold because inflammation increases mucus, which flushes out the virus.
Why
When a virus infects the nose lining, the body makes more mucus to flush out the virus. Blood vessels swell, and the nose runs.
Stages
Mucus starts clear, then turns white, yellow or green as immune cells arrive.
Color
Green mucus doesn’t always mean bacterial infection.
Duration
Colds last 7 to 10 days.
Relief
Fluids, saline spray and rest.
See a doctor
If symptoms last over 10 days, or fever is high.
Mechanism and timeline
The nose runs during a cold because viral infection triggers inflammation. Blood vessels dilate and mucus glands produce more fluid to flush out virus. Colds are caused by more than 200 viruses, most often rhinoviruses, which account for 30 to 50 percent of colds. Adults average 2 to 3 colds per year, and children 6 to 8.
- Days 1 to 3: clear, watery discharge, sneezing, sore throat.
- Days 3 to 5: mucus thickens and may turn white, yellow or green due to white blood cells, not necessarily bacterial infection.
- Symptoms generally last 7 to 10 days, with cough lingering up to 2 to 3 weeks.
Relief and when to see a doctor
Fluids, rest, saline spray or rinses with distilled water, and humidified air help. Decongestants and antihistamines give limited relief in children and are not advised for children under 4 by the FDA. Antibiotics do not treat colds. See a doctor for fever over 39 C (102 F), symptoms beyond 10 days, severe sinus pain, wheezing or difficulty breathing.
Mechanism and timeline
A runny nose in a cold is caused by inflammation that makes the nasal lining produce more mucus. Colds usually last 7 to 10 days and clear mucus may turn yellow or green normally.
Relief
Use fluids, saline spray and rest. See a doctor for fever over 3 days, symptoms over 10 days or severe sinus pain.
Immune response and mucus
Rhinovirus inflames nasal tissue, and the lining releases kinins and histamine, which cause dilated vessels and fluid leak. Nose runs clear at first, then thicker. Color change to yellow or green reflects white blood cells and does not alone indicate bacteria. Adults have about 2 to 3 colds a year.
Practical relief
Saline irrigation with distilled or boiled water, humidified air and fluids help. Ipratropium nasal spray cuts runny nose in trials. Decongestant pills such as pseudoephedrine can raise blood pressure. Antibiotics do not treat colds. Seek care if fever lasts more than 3 days, face pain develops or symptoms worsen after 10 days.
Based on data from the CDC and the Mayo Clinic
