Runny nose
A runny nose (rhinorrhoea) is excess nasal discharge, most often from a common cold or allergies. It is usually harmless and self-limiting. The colour of the discharge is a poor guide to whether antibiotics are needed; the pattern and accompanying symptoms are more useful.
What it means
A runny nose is one of the most common of all symptoms: the nasal lining produces extra mucus, which drips from the nose or down the back of the throat. By far the commonest causes are viral upper respiratory infections (the common cold and similar viruses, including the early phase of COVID-19), where the runny nose comes with sneezing, a blocked nose, sore throat and mild malaise and clears within a week or so. The other very common cause is allergy (allergic rhinitis or 'hay fever'), where the discharge is typically clear and watery and comes with sneezing, itchy eyes and a blocked nose, triggered by pollen, dust mites or animals, and often seasonal or exposure-related. Other causes include irritants (smoke, cold air, strong smells), a non-allergic sensitive nasal lining, and — with a persistently blocked and runny nose over weeks — sinus inflammation or nasal polyps. A watery runny nose after a head injury is a specific warning that needs urgent attention. The colour of the mucus (clear, yellow or green) is not a reliable sign of a bacterial infection and does not by itself mean antibiotics are needed.
Common causes
- The common cold and other viral infections — including the early phase of COVID-19; with sneezing, a blocked nose and sore throat.
- Allergic rhinitis (hay fever) — clear watery discharge with sneezing and itchy eyes; from pollen, dust mites or animals.
- Irritants — smoke, cold air, strong smells.
- Non-allergic rhinitis — a sensitive nasal lining without a clear allergy.
- Sinus inflammation (sinusitis) or nasal polyps — with a persistent blocked, runny nose.
Lab work-up approach
A runny nose rarely needs any tests — a cold is diagnosed clinically and settles on its own, and allergy is often recognised from the pattern (seasonal, with sneezing and itchy eyes). When allergy is suspected and worth confirming, allergy testing — a total IgE, specific IgE blood tests, and sometimes a raised eosinophil count — can help identify triggers. If a viral respiratory infection such as COVID-19 is in question, a viral swab, not a blood test, is what confirms it. Persistent symptoms over weeks may prompt assessment for sinus problems or polyps. Mediora.AI can surface an allergy pattern (IgE and eosinophils) when relevant and show it in context, but a runny nose is usually a simple, self-limiting symptom; persistent or unusual cases are assessed by your doctor.
Tests Mediora.AI can interpret
Related conditions
Panels to consider
When to see a doctor
A runny nose from a cold or seasonal allergy usually just needs simple measures — rest and fluids for a cold, and antihistamines or steroid nasal sprays for allergy — and settles without tests. See a doctor if a runny nose persists for many weeks, is always one-sided, comes with significant facial pain or pressure and fever (suggesting a sinus infection), or if allergy symptoms are troublesome enough to affect sleep or daily life and might benefit from targeted treatment. Seek urgent attention for a persistent watery discharge from one nostril after a head injury, which can rarely be leaking fluid from around the brain. Mediora.AI helps surface an allergy pattern when relevant; assessing a persistent or unusual runny nose is done by your doctor.