Sinusitis: acute, chronic, and why most cases don't need antibiotics

What sinusitis actually is

Sinusitis — more accurately called rhinosinusitis — is inflammation of the air-filled cavities behind the cheeks, forehead, between the eyes, and deeper in the skull base. These spaces, called the paranasal sinuses, connect to the nasal passages through narrow drainage channels. When the lining swells from a viral infection, allergies, or other triggers, those drainage channels block, mucus builds up, and the typical symptoms develop: a blocked nose, thick discharge, facial pressure or pain, and a reduced sense of smell.

The condition divides into three main categories defined by how long symptoms have been present. Acute rhinosinusitis lasts less than 12 weeks — the vast majority of these episodes are viral. Chronic rhinosinusitis lasts 12 weeks or longer and is mostly driven by ongoing inflammation rather than active infection. Recurrent acute rhinosinusitis is defined as four or more separate acute episodes per year with symptom-free intervals in between.

The condition is common. Acute sinusitis is one of the most frequent reasons people are prescribed antibiotics in Australian general practice — yet most of those prescriptions are arguably unnecessary, because around 98% of acute episodes are viral. Chronic rhinosinusitis affects an estimated 6 to 10% of Australian adults. Around 20 to 40% of people with chronic sinusitis also have asthma — the two conditions share inflammatory pathways and tend to influence each other.

Acute vs bacterial vs chronic — telling them apart

Acute viral rhinosinusitis (the common cold extending)

Most acute sinusitis starts as a viral upper respiratory infection — rhinovirus, coronavirus, influenza, RSV, or similar — that produces nasal congestion, runny nose, facial pressure, sneezing, and mild facial discomfort. Symptoms typically peak around days 3 to 5 and then gradually improve over 7 to 14 days. Coloured or thick nasal mucus by itself does not mean bacterial infection — it simply reflects the body’s inflammatory response.

Acute bacterial rhinosinusitis (the minority that needs antibiotics)

The eTG guidelines and the Australian Prescriber review on treating acute sinusitis describe specific clinical criteria for suspecting bacterial sinusitis. Antibiotics are considered when:

• Symptoms have persisted for 10 days or more without any improvement, OR
• Symptoms are severe from the start (fever above 39°C, severe facial pain, purulent unilateral discharge), OR
• Symptoms initially improved and then clearly worsened around days 5 to 7 — known as “double sickening”, OR
• The person is significantly immunocompromised, OR
• There are signs of complication.

If none of these are present, the episode is almost certainly still viral and antibiotics do not help.

Chronic rhinosinusitis (12 weeks or more)

Chronic sinusitis is defined by at least two of the following symptoms lasting 12 weeks or longer: nasal blockage, nasal discharge or post-nasal drip, facial pain or pressure, and reduced sense of smell. Diagnosis usually requires examination by an ENT specialist using a nasendoscope (a thin flexible camera) or a CT scan to confirm objective evidence of inflammation. Chronic sinusitis subdivides further — most commonly into chronic rhinosinusitis with nasal polyps (CRSwNP) and without nasal polyps (CRSsNP).

What causes it

For acute sinusitis, the trigger is almost always a viral respiratory infection. Less commonly, bacteria can be the primary cause, or a viral infection becomes complicated by a secondary bacterial overgrowth.

Chronic sinusitis usually involves a mix of factors:

• Allergic rhinitis — ongoing nasal allergy keeps the lining inflamed and the drainage channels narrow.
• Asthma — shares inflammatory pathways with the upper airway.
• Anatomical factors — a deviated nasal septum, narrow drainage passages, or nasal polyps.
• Smoking and environmental irritants — including occupational dust and chemical exposures.
• Dental disease — an abscess in an upper back tooth can spread inflammation into the maxillary sinus.
• Immune system issues — both deficiency and overactive type-2 inflammation.
• Gastro-oesophageal reflux — acid reaching the upper airway can contribute.

Risk factors that increase the chance of complicated or severe disease include diabetes, immunosuppression (from medication or disease), cystic fibrosis, and primary ciliary dyskinesia — a rare inherited disorder affecting the tiny hair-like cells that clear mucus.

Diagnosis — usually clinical, rarely imaging

Acute sinusitis is diagnosed clinically — your GP asks about symptom pattern, duration, and severity, and examines your nose, throat, ears, and face. Imaging is generally not needed for uncomplicated acute sinusitis. Plain sinus X-rays are no longer used — they are inaccurate and have been superseded by clinical assessment and, where needed, CT scans.

For chronic sinusitis, a more detailed workup is helpful and usually involves an ENT specialist:

• Nasendoscopy — a thin flexible camera passed into the nose to look directly at the drainage areas and any polyps.
• CT scan of the sinuses — the gold-standard imaging when chronic sinusitis is suspected or for pre-surgical planning.
• Allergy testing — skin prick testing or specific IgE blood tests if allergy is contributing.
• Selected blood tests — to look for immune deficiencies, eosinophil-driven inflammation, or rare conditions such as granulomatosis with polyangiitis.

CT scans involve radiation exposure and are not used routinely for uncomplicated acute sinusitis. Your GP will arrange imaging only when the clinical picture warrants it.

Treatments — what actually helps

Saline nasal irrigation

High-volume saline rinses are one of the most effective and underused treatments for both acute and chronic sinusitis. The 2016 Cochrane review found symptom benefit for chronic rhinosinusitis with low risk of harm. Use a squeeze bottle, neti pot, or sinus rinse kit (commercial AU brands include NeilMed and FLO).

Key practical points:

• Use sterile or freshly boiled and cooled water — tap water carries a rare but serious risk of amoebic infection.
• Add the saline sachet provided with the kit, or a measured mix of salt and sodium bicarbonate.
• Tilt your head forward over the sink and gently squeeze into the upper nostril; the water drains out the lower nostril.
• Use it once or twice daily for acute symptoms and twice daily for ongoing chronic sinusitis.
• Replace the bottle every one to two months and clean it after each use.

Intranasal corticosteroid sprays

Intranasal corticosteroid sprays — such as mometasone, fluticasone, and budesonide — reduce inflammation in the lining of the nose and sinuses. A 2013 Cochrane review found modest symptom benefit in acute sinusitis. For chronic sinusitis, these sprays are the cornerstone of long-term management — used daily, sometimes at higher specialist-supervised doses.

Many of these sprays are available over the counter in Australia, but it is worth speaking with your GP for personalised advice and correct technique. Aim the spray slightly outward — away from the central septum — to reduce dryness and minor nosebleeds.

Simple symptom relief

• Paracetamol or anti-inflammatory pain relief (such as ibuprofen) — for facial pain, headache, and fever. Check with your pharmacist or GP if you have other medical conditions.
• Topical decongestants (oxymetazoline, xylometazoline) — useful for short-term relief of severe blockage but must not be used for more than 3 to 5 days because of rebound congestion (called rhinitis medicamentosa).
• Oral pseudoephedrine — available behind the pharmacy counter; avoid in high blood pressure, heart disease, and the first trimester of pregnancy.
• Steam inhalation, hydration, rest, and warm compresses — all reasonable supportive measures.

Antibiotics — when and why

For acute sinusitis, antibiotics are reserved for the minority of cases that meet the bacterial criteria above. The 2018 Cochrane review on antibiotics for acute rhinosinusitis found only modest overall benefit, with side effects (diarrhoea, rash, allergic reactions) and the broader cost of antibiotic resistance to weigh against it.

When antibiotics are warranted, the first-line choice in Australia per eTG guidelines is usually amoxicillin, with amoxicillin-clavulanate or doxycycline as alternatives depending on circumstances. Courses are short — typically 5 to 7 days. Your GP will choose the right antibiotic and duration based on individual circumstances, allergies, and previous antibiotic use. NPS MedicineWise provides Australian antimicrobial stewardship guidance for both clinicians and patients.

For chronic sinusitis, routine antibiotics are not used. The condition is largely driven by inflammation rather than active infection, and biofilms in the sinus lining make it less responsive to antibiotics anyway.

When more is needed

For chronic sinusitis that does not respond to saline plus a nasal steroid spray over 4 to 8 weeks, your GP will usually refer to an ENT specialist. Options at that point include:

• A short course of oral corticosteroid tablets for severe flare-ups (limited to 1 or 2 courses per year).
• Functional endoscopic sinus surgery (FESS) — keyhole surgery to widen drainage pathways or remove polyps.
• For severe chronic sinusitis with nasal polyps, newer biologic medications such as dupilumab are available through specialists under strict Authority criteria. These target the inflammatory pathways driving polyp growth.

When to see your GP

Book a GP review if you have:

• Symptoms lasting more than 10 days without improvement.
• Worsening after initial improvement (double sickening).
• High fever (above 39°C) with severe facial pain.
• Frequent recurrence (four or more episodes per year).
• Persistent symptoms only on one side.
• Symptoms lasting more than 12 weeks (chronic sinusitis assessment).
• A weakened immune system and any sinus symptoms.
• Worsening sinusitis during pregnancy, where prescribing choices are more nuanced.

HealthDirect’s sinusitis page and the Better Health Channel sinusitis page provide additional Australian patient-friendly information.

Red flags — go to ED now

Some complications of sinusitis are rare but serious, and need emergency hospital care. Go to your nearest emergency department, or call 000 in Australia, if you develop any of these:

• Swelling, redness, or pain around the eye — possible orbital cellulitis.
• Changes in vision — blurred or double vision, reduced vision, or eye movement problems.
• Severe headache with neck stiffness, confusion, drowsiness, or fever — possible meningitis or intracranial extension.
• Weakness, numbness, slurred speech, or a focal neurological problem.
• Seizures.
• Swelling that spreads rapidly across the face or forehead.
• Black or dark patches inside the nose — particularly in people with diabetes or weakened immunity, this can indicate invasive fungal infection (mucormycosis), which is a surgical emergency.
• Persistent unexplained nosebleeds with facial numbness — needs urgent investigation for less common but serious causes.

These complications are uncommon, but recognising them early matters. When in doubt, get assessed.

What this article is and is not

This is general health information based on current Australian clinical guidelines — including Therapeutic Guidelines (eTG), Australian Prescriber, the Australian Medicines Handbook, ASCIA, and NPS MedicineWise, supported by Cochrane systematic reviews. It is not personal medical advice and does not create a doctor–patient relationship. Treatment decisions — including whether antibiotics, imaging, or specialist referral are appropriate for your situation — are made with your own GP based on your individual circumstances.

For Australian consumer-friendly information: HealthDirect — Sinusitis · Better Health Channel — Sinusitis · ASCIA.

Sources cited

1. Therapeutic Guidelines (eTG) — Acute and chronic rhinosinusitis
2. Australian Prescriber — Treating acute sinusitis
3. Australian Medicines Handbook
4. ASCIA — Chronic rhinosinusitis with nasal polyposis
5. NPS MedicineWise — antimicrobial stewardship
6. HealthDirect — Sinusitis
7. Better Health Channel — Sinusitis
8. Lemiengre Cochrane — antibiotics for acute rhinosinusitis (2018)
9. Chong Cochrane — saline irrigation for chronic rhinosinusitis (2016)
10. Zalmanovici Trestioreanu Cochrane — intranasal steroids for acute sinusitis (2013)