Cold & Flu
Symptoms, Causes & Treatment
Everything you need to know about colds and flu: what causes them, how to tell them apart, and when to seek treatment.
What Is a Cold or Flu?
The common cold and influenza (flu) are both viral respiratory illnesses that affect millions of people in the UK every year, particularly during the autumn and winter months. While they share some overlapping symptoms, they are caused by different viruses, differ significantly in severity, and carry different risks – particularly for vulnerable groups.
The common cold is caused by one of over 200 different viruses, with rhinoviruses responsible for the majority of cases. It is a mild, self-limiting illness that primarily affects the nose and throat. Most healthy adults recover fully within 7–10 days without any medical treatment.
Influenza is caused by the influenza A or B virus and is a considerably more serious illness. It tends to have a more abrupt onset, more pronounced systemic symptoms (such as high fever, severe muscle aches, and profound fatigue), and carries a real risk of serious complications – including pneumonia, hospitalisation, and death – particularly in older people, young children, pregnant women, and those with underlying health conditions.
Both illnesses are spread primarily through respiratory droplets produced when an infected person coughs, sneezes, or talks, as well as through contact with contaminated surfaces followed by touching the eyes, nose, or mouth.
Neither colds nor flu are caused by bacteria, which means antibiotics will not treat either illness. However, antiviral medications are available for flu and may be prescribed by a clinician in certain circumstances to reduce the duration and severity of the illness.
What Are the Symptoms of a Cold or Flu?
Symptoms differ considerably between the two conditions in terms of onset, severity, and which body systems are affected.
- Gradual onset over one to two days
- Runny or blocked nose (nasal congestion)
- Sneezing
- Sore or scratchy throat
- Mild dry cough
- Mild fatigue or feeling run-down
- Low-grade fever (more common in children)
- Watery eyes
- Sudden onset, often within hours
- High fever (typically 38–40°C) with chills
- Severe muscle aches and joint pain
- Intense headache
- Pronounced fatigue and weakness
- Dry, persistent cough
- Sore throat
- Loss of appetite
- Occasionally nausea, vomiting, or diarrhoea (more common in children)
Seek same-day medical attention if you or someone you care for develops difficulty breathing or shortness of breath, chest pain or tightness, persistent high fever not responding to paracetamol or ibuprofen, symptoms that improve then suddenly worsen again, or a severe headache with neck stiffness. These may indicate pneumonia, secondary bacterial infection, or another serious complication.
What Causes a Cold or Flu?
Both illnesses are caused by viruses transmitted person-to-person via respiratory droplets and contaminated surfaces. They are not caused by cold weather, though winter conditions drive people indoors and facilitate transmission.
Over 200 different viruses can cause the common cold, with rhinoviruses responsible for the majority of cases. Infection spreads via droplets from coughs and sneezes, or by touching contaminated surfaces and then the face.
Flu is caused by influenza A or B viruses, which mutate regularly — the reason annual vaccination is required. It spreads rapidly through respiratory droplets produced by coughing, sneezing, or talking.
Stress, sleep deprivation, poor nutrition, and underlying health conditions can reduce immune resilience, making individuals more susceptible to both cold and flu viruses.
Workplaces, schools, public transport, and care homes create conditions where viruses spread efficiently, particularly in poorly ventilated indoor environments during autumn and winter.
Annual influenza vaccination significantly reduces the risk of contracting flu and its complications. Uptake remains incomplete in many eligible groups, contributing to seasonal flu burden.
Infants, young children, and older adults have less robust immune responses, making them more susceptible to infection and at greater risk of complications from both conditions.
Key Risk Factors
How Is a Cold or Flu Diagnosed?
In most cases, a cold or flu is diagnosed clinically, based on the pattern and timing of symptoms. Laboratory testing is not routinely required for otherwise healthy adults with typical presentations.
How Are a Cold and Flu Treated?
The cornerstone of cold management is supportive care. Flu in high-risk individuals may also benefit from antiviral medication, which must be started promptly to be effective.
Supportive Measures
Rest and adequate hydration are the most important things you can do when unwell with a cold or flu. Aim for at least two litres of fluids per day — water, diluted juice, or clear broths are all suitable. Honey and lemon in warm water can soothe a sore throat, though this does not treat the infection. Antibiotics are ineffective against viral infections and should not be requested or taken for a straightforward cold or flu unless a bacterial complication is confirmed.
Influenza Vaccination
Annual flu vaccination is the single most effective measure for preventing influenza and its complications. The NHS offers free vaccination to all eligible groups including adults aged 65 and over, pregnant women, children aged 2–17 (nasal spray), and individuals with certain long-term health conditions. Even if you have had flu before, vaccination each year is recommended as circulating strains change. Private vaccination is available to those outside NHS-eligible groups.
When Should You Seek Medical Advice for a Cold or Flu?
You or someone you care for has difficulty breathing or is breathing very rapidly · There is persistent chest pain or pressure · The person is confused, unresponsive, or cannot be roused · Lips or fingernails appear blue (cyanosis) · A child is breathing rapidly, has a high-pitched noise when breathing, or has a seizure.
Symptoms are severe, rapidly worsening, or not improving after seven days · You have a high fever not responding to paracetamol or ibuprofen · You are in a high-risk group (pregnant, over 65, have a chronic health condition, or are immunocompromised) and have flu symptoms — antiviral treatment must be started within 48 hours · You suspect a secondary bacterial infection such as sinusitis, ear infection, or pneumonia · A child under six months has a fever or appears unwell.
How Can You Prevent Colds and Flu?
While no measure guarantees complete protection, a combination of vaccination, good hygiene, and healthy habits significantly reduces the risk of infection and transmission.
Vaccination is the most effective way to protect yourself and others against influenza. Even partial immunity reduces severity and complications.
Handwashing with soap and water for at least 20 seconds is highly effective at removing viruses, particularly after coughing, sneezing, or contact with shared surfaces.
Use a tissue or the inside of your elbow. Dispose of tissues immediately and wash your hands. This significantly reduces the number of viral particles released into the air.
Viruses enter the body through the eyes, nose, and mouth. Minimising face-touching, especially with unwashed hands, reduces this transmission route.
Opening windows regularly, even briefly, reduces the concentration of airborne viral particles in rooms where multiple people spend time together.
Regular physical activity, adequate sleep (7–9 hours for adults), a balanced diet, and avoiding smoking all contribute to a more robust immune response.
Speak to a Clinician About Cold and Flu
Getting treatment for cold and flu symptoms no longer means waiting days for a GP appointment. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If antiviral treatment or another prescription is clinically appropriate, it will be sent to your pharmacy the same day.
Expert clinical advice, when you need it.
Cold & Flu FAQs
The key difference is the onset and severity of symptoms. A cold develops gradually over one to two days with predominantly nasal symptoms — congestion, runny nose, and sneezing — with little or no fever. Flu comes on suddenly, often within hours, with a high fever, intense muscle aches, severe fatigue, and headache. If you feel well enough to go about your day, it is likely a cold. If you feel too unwell to get out of bed, it is more likely flu. A clinician can help confirm the diagnosis if you are uncertain.
No. Colds and flu are caused by viruses, and antibiotics only work against bacterial infections. Taking antibiotics when they are not needed does not shorten illness duration, does not relieve symptoms, and contributes to antibiotic resistance. If a secondary bacterial infection develops — such as a chest infection, sinusitis, or ear infection — a clinician will assess whether antibiotic treatment is appropriate.
Oseltamivir (Tamiflu) is a prescription antiviral medication that can reduce the duration and severity of flu if started within 48 hours of symptom onset. It is most beneficial for high-risk individuals — those aged over 65, pregnant women, or people with chronic health conditions. For otherwise healthy adults with uncomplicated flu, the benefit is more modest. A clinician can assess whether it is appropriate for you.
Most colds resolve within seven to ten days, though a cough or runny nose may linger for up to two weeks. Flu symptoms — particularly fatigue and weakness — can persist for two to three weeks, even after the acute phase has passed. If symptoms are worsening after the first week rather than improving, seek clinical advice.
With a cold, you are typically most contagious in the first two to three days of symptoms, though you can pass the virus on from around 24 hours before symptoms appear until about a week after they start. Flu is contagious from around one day before symptoms develop until five to seven days after symptom onset. Children may be contagious for longer. Stay home where possible during this period to protect others.
Light activity may be tolerable if you have mild cold symptoms confined to the nose and throat. However, if you have flu, a fever, chest symptoms, significant fatigue, or muscle aches, rest is strongly recommended. Exercising with flu-like symptoms places unnecessary strain on the body and may worsen or prolong illness.
The evidence is modest. High-dose vitamin C has not been shown to prevent colds in the general population, though it may very slightly reduce duration in some people. Zinc lozenges, taken at the onset of symptoms, may reduce the duration of a cold by a day or so when started within 24 hours. Neither replaces adequate rest, hydration, and general immune health as the primary defence.
Yes. The annual flu vaccine is safe, well-tolerated, and recommended each year because influenza viruses mutate and circulating strains change. Immunity from the previous year’s vaccine may not protect against the current season’s strains. Side effects are typically mild and short-lived — a sore arm, mild fatigue, or low-grade fever for one to two days.