Sinusitis — Symptoms, Causes & Treatment | MyMedicPlus

Sinusitis, more precisely termed rhinosinusitis (RS), is inflammation of the mucosal lining of the paranasal sinuses (maxillary, ethmoid, frontal, and sphenoid) occurring in conjunction with nasal cavity inflammation. It is classified by duration: acute rhinosinusitis (ARS — less than 4 weeks, most often viral); subacute (4–12 weeks); recurrent acute sinusitis (four or more episodes per year, each lasting less than 4 weeks); and chronic rhinosinusitis (CRS — symptoms persisting for 12 weeks or more despite treatment). CRS is further classified into CRS with nasal polyps (CRSwNP — associated with type 2 eosinophilic inflammation, frequently with concurrent asthma and aspirin sensitivity — Samter's triad) and CRS without nasal polyps (CRSsNP). Sinusitis is one of the most common conditions in primary care — affecting approximately 1 in 8 adults per year, accounting for approximately 1% of all GP consultations globally, and one of the most frequently cited justifications for antibiotic prescribing. Critically, 80–90% of acute episodes are caused by respiratory viruses (rhinovirus, coronavirus, influenza, adenovirus) and are self-limiting within 7–10 days without antibiotics. Only approximately 0.5–2% of viral upper respiratory infections are complicated by secondary bacterial sinusitis — systematic over-prescribing of antibiotics for viral sinusitis is a major contributor to antimicrobial resistance globally and should be actively avoided.

Viral upper respiratory tract infections (URTI): the most common trigger of acute sinusitis — rhinovirus, influenza, parainfluenza, respiratory syncytial virus, and coronaviruses cause mucosal oedema, cilia dysfunction, and impaired mucociliary clearance, creating conditions for bacterial superinfection. Secondary bacterial (post-viral) acute sinusitis: predominantly caused by Streptococcus pneumoniae (approximately 30–40% of bacterial cases), Haemophilus influenzae (approximately 20–30%), Moraxella catarrhalis (approximately 20%), and occasionally Streptococcus pyogenes and Staphylococcus aureus; anaerobes (in odontogenic sinusitis). Risk factors for chronic rhinosinusitis (CRS): allergic rhinitis (the most important predisposing factor for CRS — chronic mucosal oedema obstructs the osteomeatal complex, impairing sinus drainage); nasal polyps (type 2 eosinophilic mucosal disease — often with concurrent asthma and aspirin-exacerbated respiratory disease); deviated nasal septum or other anatomical variants (concha bullosa, Haller cells) impairing drainage; primary immunodeficiency (IgA deficiency, common variable immunodeficiency/CVID, and hypogammaglobulinaemia — recurrent bacterial sinusitis a common presentation); cystic fibrosis (abnormal mucus composition and cilia dysfunction cause pansinusitis in virtually all patients); primary ciliary dyskinesia (Kartagener syndrome — immotile cilia); asthma (co-exists with CRS in approximately 25–30%); gastro-oesophageal reflux disease (GERD — acid microaspiration may irritate the sinonasal mucosa); and odontogenic sinusitis — infection of the upper posterior teeth (particularly the second premolar and first and second molars, whose roots may protrude into the maxillary sinus floor) causing maxillary sinusitis, accounting for up to 20% of all maxillary sinusitis cases — commonly missed.

The cardinal symptoms of rhinosinusitis (EPOS 2020 criteria) are: nasal blockage or congestion, and/or nasal discharge (anterior, or post-nasal drip — dripping down the back of the throat), accompanied by facial pain, pressure, or fullness, and/or hyposmia or anosmia (reduced or absent sense of smell — characteristic of CRS with nasal polyps). Location of facial pain varies by sinus involved: maxillary sinusitis — pain or pressure over the cheeks, upper teeth, and below the eyes (often worsened by bending forward); frontal sinusitis — forehead pain and pressure, particularly in the morning; ethmoid sinusitis — pain between and behind the eyes; sphenoid sinusitis — deep retro-orbital or vertex (top-of-head) pain. Additional symptoms: purulent (yellow or green) nasal or post-nasal discharge, headache, low-grade fever (more common in bacterial sinusitis — high fever above 38.5°C is a 'red flag' for bacterial or complicated sinusitis), cough (particularly nocturnal post-nasal drip), halitosis (bad breath — from stagnant infected secretions), and dental pain (odontogenic involvement or referral from maxillary sinus). 'Double sickening': the pattern where initial viral rhinitis symptoms begin to improve after 5–6 days, then suddenly worsen with increasing pain, fever, and more purulent discharge — this is the most reliable clinical sign of bacterial superinfection and is a key indication to consider antibiotic treatment. Chronic rhinosinusitis (CRS): symptoms present for 12 weeks or more — typically more dominated by nasal obstruction, post-nasal drip, hyposmia/anosmia, and nasal polyps (in CRSwNP) than by acute facial pain.

Acute sinusitis is a clinical diagnosis — investigations are not required for typical uncomplicated presentations. Diagnostic criteria for acute bacterial rhinosinusitis (EPOS 2020): symptoms for more than 10 days without improvement; or 'double sickening' (worsening after initial partial improvement around days 5–6); or severe symptoms from the outset with high fever (above 38.5°C), severe unilateral facial pain, and purulent nasal discharge. Plain X-rays are not recommended — they have poor sensitivity and specificity and should not be used routinely. CT sinuses (Hounsfield units of soft tissue mucosal thickening, air-fluid levels, osteomeatal complex obstruction, bony wall integrity): the gold standard for CRS evaluation and pre-surgical planning — not indicated for acute uncomplicated sinusitis; reserved for CRS not responding to treatment, suspected complications (orbital, intracranial spread), and pre-FESS anatomical assessment. Nasal endoscopy (rigid or flexible 0-degree endoscope): visualises the middle meatus — the ostiomeatal complex — for mucosal oedema, polyps, purulent discharge, and anatomical variants; essential in specialist ENT assessment of CRS. Microbial culture of middle meatal secretions (by endoscopically-guided swab): indicated in CRS with refractory infection, immunocompromised patients, and when an unusual or resistant organism is suspected. Allergy testing (skin prick testing or RAST/specific IgE blood tests): for CRS patients with suspected allergic rhinitis as the underlying driver. Blood tests: FBC, immunoglobulins (IgG, IgA, IgM, IgE), specific antibody responses (Streptococcus pneumoniae vaccine response) — for suspected primary immunodeficiency in patients with recurrent bacterial sinusitis. Cystic fibrosis sweat test and genetics: in young patients with pansinusitis.

Viral acute sinusitis (the majority — 80–90% of cases — are viral and self-limiting within 7–10 days): the cornerstone of management is symptom relief and avoidance of unnecessary antibiotics. High-volume saline nasal irrigation (240 mL warm isotonic or hypertonic saline — neti pot, squeeze bottle, or nasal rinsing device): clears mucus, reduces mucosal oedema, improves mucociliary clearance, and significantly reduces symptom burden and duration — recommended as first-line self-care. Intranasal corticosteroids (INCS — mometasone 200 mcg daily or fluticasone furoate 110 mcg daily): have modest but significant benefit in acute sinusitis — reduce mucosal oedema, facilitate sinus drainage, and reduce symptom duration; use for at least 2–4 weeks. Analgesics (paracetamol and ibuprofen): for facial pain and headache relief. Decongestants (oxymetazoline 0.05% nasal spray): short-term use only (maximum 5–7 days) to relieve nasal congestion — avoid prolonged use due to rhinitis medicamentosa (rebound congestion). Antihistamines: only if concurrent allergic rhinitis — little benefit in purely infective sinusitis. Bacterial acute sinusitis: antibiotic treatment is justified when clinical criteria are met (NICE recommends a back-up antibiotic prescription strategy for 5–10 days before filling, unless severe); first-line — amoxicillin-clavulanate (co-amoxiclav) 500/125 mg three times daily for 5–7 days; second-line or penicillin allergy — doxycycline 200 mg day 1 then 100 mg daily for 5–7 days, or clarithromycin 500 mg twice daily. CRS management: prolonged INCS (12+ weeks minimum); 3-month course of low-dose macrolide antibiotic (azithromycin 250 mg three times per week or erythromycin 250 mg twice daily — anti-inflammatory, not purely antibacterial effect); allergen avoidance and allergen immunotherapy for allergic CRS; biological therapy — dupilumab (Dupixent — anti-IL-4/IL-13 — approved by NICE for severe CRSwNP inadequately controlled by nasal steroids and surgery) and mepolizumab (anti-IL-5). Functional endoscopic sinus surgery (FESS): for CRS refractory to maximal medical therapy — opens the osteomeatal complex, removes polyps, and improves mucociliary function; requires post-operative nasal saline irrigation and INCS maintenance.

Orbital complications (most common serious complication — from ethmoid sinusitis, which lies immediately adjacent to the orbit): preseptal (periorbital) cellulitis — periorbital oedema and erythema without proptosis (Chandler Class I — treated with IV antibiotics); orbital cellulitis (Chandler Class II — requires urgent ophthalmology, CT scan, and IV antibiotics); subperiosteal abscess (Chandler Class III — surgical drainage may be required); orbital abscess (Chandler Class IV — immediately vision-threatening from optic nerve compression and raised intraorbital pressure; requires emergency surgical drainage); and cavernous sinus thrombosis (Chandler Class V — septic thrombophlebitis of the cavernous sinus causing bilateral proptosis, ophthalmoplegia, severe headache, high fever, and systemic sepsis — a life-threatening emergency with high mortality). Intracranial complications (from frontal sinusitis — as the frontal sinus has a thin posterior wall adjacent to the dura): meningitis; epidural abscess; subdural empyema; intracerebral abscess; and superior sagittal sinus thrombosis — all requiring neurosurgical intervention. Pott's puffy tumour (osteomyelitis of the frontal bone): presents as forehead swelling, erythema, and fluctuation — requires surgical debridement and prolonged IV antibiotics. CRS-related morbidity: anosmia (severely impacting quality of life and food enjoyment and safety — inability to smell gas leaks or smoke); sleep disruption from nasal obstruction (contributing to obstructive sleep apnoea in some patients); recurrent ARS requiring repeated antibiotic courses; and significant quality-of-life impairment with fatigue, cognitive slowdown ('brain fog'), and mood disturbance.

Annual influenza vaccination: reduces incidence of influenza-triggered acute sinusitis. COVID-19 vaccination similarly reduces the frequency of viral URTI-triggered sinusitis. Treat allergic rhinitis proactively and aggressively: daily INCS (mometasone, fluticasone furoate) combined with non-sedating antihistamines (cetirizine, fexofenadine, loratadine) to reduce mucosal oedema and sinonasal congestion — the most important preventive measure for recurrent acute sinusitis in atopic individuals. Allergen immunotherapy (subcutaneous or sublingual) for those with documented aeroallergen sensitisation and inadequately controlled allergic rhinitis — reduces need for medications and frequency of sinusitis episodes. Daily nasal saline irrigation: evidence supports that twice-daily high-volume saline rinses reduce CRS symptom burden and may reduce recurrence after acute episodes by approximately 50%. Maintain adequate indoor humidity (40–60%): dry air desiccates mucosal membranes and impairs cilia function. Avoid known allergens (house dust mite, pet dander, mould) and environmental irritants (cigarette smoke — particularly harmful to sinonasal mucosal health; pollutants; occupational dusts and chemicals). Smoking cessation: smoking is associated with significantly worse CRS outcomes and post-FESS recurrence. GERD management (proton pump inhibitors, dietary modification, head-of-bed elevation): may improve sinonasal symptoms in patients with documented reflux-driven sinonasal disease. Prompt dental care: regular dental check-ups and early treatment of upper posterior tooth periapical infections or dental abscesses to prevent odontogenic maxillary sinusitis. After FESS: nasal saline irrigation twice daily starting 24–48 hours after surgery; regular ENT endoscopic follow-up at 2 weeks, 6 weeks, 3 months, and thereafter; INCS maintained long-term to reduce polyp recurrence — repeat FESS is needed in approximately 20–30% within 5 years for CRSwNP.

Attend Emergency Department immediately for signs of sinusitis complications — which, though rare, can be life-threatening: periorbital (around the eye) swelling, redness, or pain — possible orbital cellulitis or orbital abscess from ethmoid sinusitis; proptosis (eye bulging forward), double vision, or eye movement restriction — orbital abscess or cavernous sinus thrombosis; severe headache with neck stiffness, light sensitivity, or confusion — possible intracranial complication (meningitis, epidural or subdural empyema); frontal (forehead) swelling and fluctuation — possible Pott's puffy tumour (osteomyelitis of the frontal sinus bone); high fever above 39°C with toxic appearance alongside severe sinus pain. See your GP within 48 hours for: sinusitis symptoms that have clearly worsened after 5 days of onset, or persisted without improvement beyond 10 days — bacterial superinfection likely needing antibiotic review; 'double sickening' — initial improvement then sudden significant worsening (suggests secondary bacterial infection); unilateral facial pain or toothache-type pain with coloured nasal discharge — consider dental abscess-related odontogenic sinusitis; one-sided bloodstained nasal discharge or nasal blockage without a clear infectious cause — requires ENT assessment to exclude nasal or sinus malignancy. Routine GP or pharmacist advice is appropriate for mild acute sinusitis symptoms of less than 10 days with no alarming features — most resolve without antibiotics.