Short answer
Functional endoscopic sinus surgery (FESS) is an operation done through the nostrils with a thin camera (an endoscope) to widen the blocked drainage channels of the sinuses by removing small amounts of bone, swollen lining or polyps. It is used for chronic rhinosinusitis (long-term sinus inflammation) when steroid sprays, rinses and other medicines have not controlled symptoms. It improves symptoms for most people but does not cure the condition, so nasal sprays usually continue afterwards. Whether it is worth considering depends mainly on how severe symptoms are despite proper medical treatment.
Key points
- FESS is done under general anaesthetic, with no cuts on the face.
- It is usually considered after at least three months of medical treatment.
- A large UK trial found clearly better symptom scores at six months than medicines alone.
- About 1 in 8 people need another sinus operation within 5 to 10 years.
- Serious complications, such as eye injury or leakage of brain fluid, are rare.
What FESS is used for
Most sinusitis clears within four weeks. If symptoms continue after three months of treatment, a GP may refer to an ear, nose and throat (ENT) specialist.1 Long-lasting sinus inflammation is called chronic rhinosinusitis, and it can occur with or without nasal polyps (soft, non-cancerous swellings of the sinus lining).
Medical treatment comes first: steroid nasal sprays or drops, sometimes for months, saline rinses, antihistamines if allergy contributes and, occasionally, antibiotics.12 An ENT specialist may recommend surgery for some people whose symptoms persist.1
What the operation involves
FESS is performed under general anaesthetic.1 The surgeon works entirely through the nostrils with telescopes and fine instruments, so there are no external cuts or stitches. Small pieces of bone and swollen lining that block the sinuses are removed to widen their drainage.2 In some cases a small balloon is inflated in a blocked sinus to widen it and then removed.1
The aims are better sinus drainage, fewer and milder symptoms, and better delivery of nasal medicines to the sinus lining. FESS improves symptoms but does not cure chronic sinusitis.2 A septoplasty (straightening the nasal septum) is sometimes done at the same time.2
How well it works
Until recently the evidence was weak. A 2014 Cochrane review found only four small trials comparing surgery with medical treatment for chronic rhinosinusitis with polyps, and no important differences in symptoms or quality of life. The evidence was of low or very low quality, partly because the trials used outdated treatment regimens.3
The MACRO trial, published in The Lancet in 2025, changed that picture. It randomised 514 UK adults whose chronic rhinosinusitis persisted despite medical treatment to endoscopic sinus surgery, three months of the antibiotic clarithromycin, or placebo, with all groups continuing nasal steroids and saline rinses.4
| Group | Average SNOT-22 score at 6 months |
|---|---|
| Endoscopic sinus surgery | 24.3 |
| Clarithromycin | 42.8 |
| Placebo | 46.8 |
Surgery improved scores substantially more than either medicine, and 97% of surgery patients reached a clinically meaningful improvement. The benefit was seen in people with and without polyps, although the group without polyps was small. Clarithromycin was no better than placebo. The authors concluded that surgery should be recommended if nasal medicines alone cannot control symptoms.4
Taken together, the evidence that FESS improves symptoms in the following months is Moderate. Its main outcome was measured at six months, and symptoms can return: about 1 in 8 people need further sinus surgery within 5 to 10 years, and continuing nasal sprays may reduce this risk.24
Risks
In the MACRO trial, serious adverse events were rare and similar across groups (2% after surgery).4 The NHS consent form for this operation lists:2
- Common: blood-stained discharge for 1 to 2 weeks; reduced sense of smell that usually improves over weeks.
- Eye-socket bruising: minor bleeding into the eye socket is more common than eye injury and usually settles.
- Rare: significant bleeding; infection; leakage of cerebrospinal fluid (the fluid around the brain), which may need another operation and very rarely leads to meningitis; injury to the eye.
- Very rare: severe bleeding into the eye socket, causing swelling, double vision or loss of sight; permanent loss of smell.
After surgery, rinses and drops help clear crusts and dissolvable packing, and people are asked not to blow their nose, especially if there is bruising around the eye.2
When to seek medical advice
After sinus surgery, see a doctor if your nose becomes increasingly blocked or sore, or you develop a temperature. Severe swelling around the eye or double vision needs urgent assessment by an eye specialist.2
Common questions
Will I have any visible scars?
No; the operation is done entirely through the nostrils.2
Will I still need nasal sprays afterwards?
Usually yes, because surgery does not cure chronic sinusitis and sprays may lower the chance of symptoms returning.2
Is long-term antibiotic treatment an alternative?
The MACRO trial found that three months of low-dose clarithromycin was no better than placebo, and did not support its routine use.4
Is FESS the same as turbinate reduction?
No; FESS opens the sinus drainage channels,2 while turbinate reduction shrinks structures inside the nasal passage. See what turbinate reduction is.
Bottom line
FESS widens blocked sinus channels and, in recent UK trial evidence, clearly improves symptoms for people whose chronic rhinosinusitis is not controlled by nasal medicines. It is a step in long-term management rather than a cure, and its rare but serious risks are worth discussing in detail.
Related reading
Sources
- NHS. Sinusitis (sinus infection). NHS website. https://www.nhs.uk/conditions/sinusitis-sinus-infection/. Accessed 5 November 2026.
- NHS England Getting It Right First Time (GIRFT) programme. Endoscopic sinus surgery: consent form. Version 1.0; 2022. https://www.stgeorges.nhs.uk/wp-content/uploads/2024/02/DC22.016.1.6-NHS-Consent-Form_Endoscopic-Sinus-Surgery_1.pdf. Accessed 5 November 2026.
- Rimmer J, Fokkens W, Chong LY, Hopkins C. Surgical versus medical interventions for chronic rhinosinusitis with nasal polyps. Cochrane Database of Systematic Reviews; 2014, Issue 12: CD006991. https://www.cochrane.org/evidence/CD006991_surgical-versus-medical-interventions-chronic-rhinosinusitis-nasal-polyps. Accessed 5 November 2026.
- Philpott C, Beard DJ, Saeedi E, Cook JA, Jones S, et al. The clinical effectiveness of clarithromycin versus endoscopic sinus surgery for adults with chronic rhinosinusitis with and without nasal polyps (MACRO). The Lancet; 2025;406:926–39. https://eprints.soton.ac.uk/505905/1/1-s2.0-S0140673625012486-main.pdf. Accessed 5 November 2026.
Article history
- — First published.