The short version
- Antibiotics kill bacteria and have no effect on viruses
- Colds, most sore throats, most sinus infections and most bronchitis are viral
- Australia prescribes antibiotics at high rates by international comparison
- Green mucus indicates immune activity, not bacterial infection
The distinction that does all the work
Antibiotics kill bacteria. Viruses are a different kind of organism entirely, and antibiotics do nothing to them — not a little, not slowly. Nothing.
Colds, influenza, COVID-19, most sore throats, most sinus infections and most acute bronchitis are viral. So the honest answer for a large share of winter appointments is that antibiotics will not shorten the illness by a single day.
What they cost when they are not needed
Side effects are the immediate price: diarrhoea, thrush, rash, and occasionally a serious allergic reaction. Disruption to gut bacteria can last months.
The longer-term cost is resistance. Every unnecessary course selects for bacteria that survive it. Australia prescribes antibiotics at high rates compared with similar countries, and resistant infections are already harder to treat — which matters most for the people who will one day genuinely need them, including you.
The myths worth retiring
- “Green mucus means bacteria.” It means immune cells are present. Viral infections turn mucus green routinely.
- “It's lasted a week, so it must be bacterial.” Viral illnesses commonly run ten days or longer.
- “Antibiotics can't hurt.” They can, both immediately and cumulatively.
- “I'll keep the leftovers for next time.” Partial courses drive resistance, and the leftovers are rarely right for the next illness.
When they are genuinely needed
Bacterial pneumonia, urinary tract infections, cellulitis and other skin infections, some ear and throat infections, dental infections, and infections in people whose immune systems are suppressed. In those situations antibiotics are important and starting them promptly matters.
Your GP is weighing the pattern of illness, your examination and sometimes a test. A consultation that ends without a prescription is not a wasted appointment — it is often the assessment working correctly, and it comes with safety-net advice about what would change the answer.
If you are prescribed a course
Take it as directed and follow the advice you are given about completing it. Do not share it, do not save it, and tell your GP about any reaction. Return the leftovers to a pharmacy rather than the bin. See same-day appointments if you are getting worse rather than better.
Common questions
Most winter infections are viral, and antibiotics have no effect on viruses. Your GP assesses whether a bacterial infection is likely before prescribing, and will explain what would change that assessment.
No. Green mucus reflects immune cell activity and occurs routinely in viral infections.
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