Doctors should cut down on antibiotic prescriptions for a common infection because the drugs do not work, researchers say.
Sinusitis can be very painful
Around 90% of people with sinusitis in the UK are prescribed antibiotics.
But an analysis of nine trials published in The Lancet shows the drugs make no difference even if the patient has been ill for more than seven days.
Sinusitis is very common - often occurring after colds or flu - with 1-5% of adults diagnosed every year.
The infection of the sinuses - small air pockets inside the cheekbones and forehead - causes a high temperature, pain and tenderness in the face and forehead, and a blocked or runny nose.
Several guidelines advise doctors to prescribe antibiotics only when the patient has been ill for seven to 10 days.
It has been thought that this length of illness may indicate a bacterial rather than viral infection which would be susceptible to antibiotics.
The latest research, which looked at how long 2,600 patients were ill before they received treatment, found time of illness is not a good indicator of whether antibiotics will be effective.
Because of side-effects, costs, and the risk of resistance, antibiotics are not justified even if patients have been ill for longer than a week, the researchers concluded.
The figures showed 15 patients would need to be treated before one would be cured with antibiotics.
Study leader, Dr Jim Young, from the Basel Institute for Clinical Epidemiology in Switzerland, said: "If a patient comes to the GP and says they have had the complaint for seven to 10 days that's not a good enough reason for giving them the antibiotic."
He added it would be reasonable for GPs to advise patients to come back if symptoms got worse or went on for another week.
The National Institute for Clinical and health Excellence (NICE) published draft guidance this week advising GPs not to prescribe antibiotics or issue delayed prescriptions which patients can use if they do not get better.
Co-author, Dr Ian Williamson, a GP in Southampton and researcher at Southampton University, said sinusitis was a horrible condition and people expected to get antibiotics from their GP to help them.
"Antibiotics really don't look as if they work.
"We have found that antibiotics aren't effective for sore throats and ear infections but sinusitis, which is similar, is the one that people are slightly more die hard about."
Professor Steve Field, chair of the Royal College of GPs, said doctors had been working hard to reduce antibiotic use for sinusitis in recent years but there was probably still too many prescribed.
"This gives reassurance to GPs that even if patients have specific symptoms, it's unlikely antibiotics are going to make a dramatic difference."
He advised those suffering from the infection to relieve symptoms with steam, paracetamol (acetaminophen) and rest.
"You don't need to see the GP unless you've been ill for a week."