Approach to a runny nose, including CSF leak
- Approach to a complaint
Most runny noses are viral or allergic; clear, one-sided, persistent discharge means thinking of a cerebrospinal fluid leak.
What it is
Rhinorrhoea is almost always due to a viral cold or allergic rhinitis and does not need antibiotics. The approach separates infectious from allergic and non-allergic causes, and recognises bacterial rhinosinusitis by its course: it lasts more than 10 days without improving, is severe from the start or worsens after improving. One-sided discharge deserves special attention: in a child it is usually a foreign body, in an adult it may be a tumour, and if it is clear and watery, especially after trauma or surgery, it may be cerebrospinal fluid with a risk of meningitis.
Key questions in the history
- One side or both? Clear, purulent or bloody?
- Since when? Did it improve and then worsen?
- Sneezing, itching, watery eyes, triggers such as dust or animals?
- Does it increase on leaning forward or taste salty? Head injury or nasal surgery?
- Worse with cold, smells or eating?
- Topical decongestant use?
Causes and classification
- Infectious: viral common cold (the most frequent) and acute bacterial rhinosinusitis.
- Allergic: watery, with sneezing and nasal or eye itching; seasonal or perennial.
- Non-allergic: vasomotor (temperature changes, smells), gustatory (when eating) and rhinitis medicamentosa.
- One-sided: foreign body in a child, tumour in an adult, CSF leak.
- CSF leak: traumatic (skull base fracture, surgery) or spontaneous.
Step-by-step approach
- Define whether it is one-sided or bilateral, clear or purulent, and its duration.
- Look for allergic or irritant triggers, a link with meals and decongestant use.
- Classify rhinosinusitis: viral if it improves before 10 days; bacterial if it persists, is severe or worsens after improving.
- If it is clear, one-sided and increases on leaning forward, or follows trauma or surgery, collect a sample for beta-2 transferrin.
- If it is one-sided, purulent and foul in a child, look for a foreign body.
- If it is one-sided with blood or blockage in an adult, arrange nasal endoscopy to rule out a tumour.
Differential diagnosis of a runny nose
| Cause | Discharge | Key clue |
|---|---|---|
| Common cold | Clear, later thicker | Early fever if any; self-limiting course |
| Acute bacterial rhinosinusitis | Purulent | Over 10 days, severe or worse after improving |
| Allergic rhinitis | Watery, bilateral | Sneezing, itching, conjunctivitis |
| Vasomotor or gustatory rhinitis | Watery | Cold, smells or meals; no itching |
| Rhinitis medicamentosa | Variable, with congestion | Prolonged decongestant use |
| Foreign body | One-sided, purulent, foul | Young child |
| CSF leak | Clear, one-sided | Trauma or surgery; worse leaning forward; beta-2 transferrin |
Red flags
- Clear one-sided discharge after head injury or nasal surgery: CSF leak with a risk of meningitis.
- Periorbital swelling, double vision, loss of vision or severe headache: complication of rhinosinusitis.
- One-sided bloody or foul discharge in an adult.
- History of recurrent meningitis.
Next step / Initial management
- Common cold: symptomatic care; do not prescribe antibiotics.
- Uncomplicated acute bacterial rhinosinusitis: watchful waiting if follow-up is reliable; if treating, amoxicillin or amoxicillin-clavulanate.
- Allergic rhinitis: an intranasal corticosteroid first line and a second-generation antihistamine; in rhinitis medicamentosa, stop the decongestant.
- Suspected CSF leak: beta-2 transferrin, skull base CT and urgent referral to ENT or neurosurgery.
- Priority referral: one-sided bloody or obstructive discharge in an adult; urgent referral with orbital or neurological signs.
Test yourself
Think of the answer, then tap the question to see it.
Weeks after a skull base fracture, a 40-year-old man notices clear fluid dripping from the right nostril when he leans forward. Which test do you order?
Beta-2 transferrin in the fluid to confirm CSF; then skull base CT and urgent referral because of the risk of meningitis.
An adult has had purulent discharge and congestion for 5 days, without high fever. Do you prescribe an antibiotic?
No. It is most likely viral; bacterial infection is suspected if it lasts more than 10 days without improving, is severe or worsens after improving.
What is the first-line treatment of allergic rhinitis?
An intranasal corticosteroid, with a second-generation antihistamine as symptoms require.
A 3-year-old girl has had purulent, foul discharge from the left nostril for 10 days. What do you suspect?
A nasal foreign body: one-sided foul discharge in a young child suggests it.
Connections
Educational content; it does not replace a medical assessment and is not a clinical instruction. For a real case, follow current guidelines and specialist advice.
Sources: Allergic Rhinitis (StatPearls Publishing (NCBI Bookshelf), 2023); Rhinitis Medicamentosa (StatPearls Publishing (NCBI Bookshelf), 2026); Cerebrospinal Fluid Leak (StatPearls Publishing (NCBI Bookshelf), 2025); Outpatient Clinical Care for Adults (Centers for Disease Control and Prevention (CDC), 2024); Outpatient Clinical Care for Pediatric Populations (Centers for Disease Control and Prevention (CDC), 2024); Acute Sinusitis (StatPearls Publishing (NCBI Bookshelf), 2025); Nasal Foreign Body (StatPearls Publishing (NCBI Bookshelf), 2023).
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Representative model, for educational purposes only.