Cold or flu? How to tell the difference in symptoms

You woke up feeling rough, and now you are deciding whether to push through the day or write it off entirely. Colds and flu are caused by different viruses, they behave differently once they take hold, and working out which one you have tells you roughly what the next week looks like.

Nobody can separate the two from a single symptom. Plenty of colds come with a mild temperature, and plenty of people call any miserable cold "the flu". But there is a pattern that holds up most of the time, and the pattern is usually enough to plan around.

Two different families of virus

A cold is caused by one of a large group of viruses, rhinoviruses most often, and it tends to stay in your nose and throat. That is why the main event is a blocked or streaming nose, sneezing and a scratchy throat, while the rest of you carries on more or less functioning.

Influenza is a different animal. It affects the whole body, which is why the aching, the shivering and the flattened, cannot-lift-my-head exhaustion are the parts people remember years later. Respiratory symptoms are there too, but on day one they are often not the worst of it.

One thing applies to both. Antibiotics do nothing for either, because they only kill bacteria and these are viruses from beginning to end. They will not shorten a cold and they will not stop a flu. Occasionally a bacterial infection develops on top of a viral one, and that is a different situation, which is where an assessment of cold and flu symptoms earns its keep.

Onset speed is the biggest single clue

Ask yourself how the illness arrived. A cold creeps up on you. There is a tickle in your throat in the afternoon, you are snuffly by bedtime, and next morning you know what you have got. Flu does not creep. People can often name the hour: fine at eleven, under a blanket with their teeth chattering by two.

What you notice	Common cold	Flu
How it starts	Gradually, over a day or two	Suddenly, often within hours
Fever	Mild or absent	Common, with shivering and sweats
Body aches	Mild if any	Prominent, including back, legs and shoulders
Exhaustion	You feel below par but function	You can do very little for several days
Blocked or runny nose	Usually the main symptom	Present but less dominant early on
Cough	Tickly, tends to arrive later	Dry and tiring, often from the start
Back to normal	About a week, cough outstays it	A week floored, then a week or two of low energy

Treat that as a guide rather than a diagnosis. Older adults, people who are pregnant and anyone with a long-term lung, heart or immune condition can have flu without a dramatic fever, so a mild-looking illness in those groups deserves more attention rather than less.

Symptoms that shift the picture

Alongside the usual suspects, some details change what a doctor thinks is going on, and they are the ones you will be asked about:

• A throat so raw that swallowing your own saliva is unpleasant happens with either, but a high temperature with swollen glands and no cough at all can mean tonsillitis rather than a simple cold.
• Pressure across your cheeks and forehead that worsens when you bend forwards, especially after a cold that had begun to improve, suggests the sinuses have become involved.
• A cough that becomes the dominant symptom and starts producing phlegm as the rest of you improves looks more like a chest infection.
• Wheeze, tightness, or needing your reliever inhaler far more than usual, which needs same-day attention if you have asthma.

How long each one lasts, and what helps

Most colds are done in about a week, although the cough and the last of the congestion often hang on after you feel basically well. Flu is slower. The worst lasts several days, the fever settles within a few days to a week, then comes a tail of tiredness that can run on for a fortnight. That tail catches people out, because they return to full tilt too early and get knocked flat again.

At home, the boring measures are the ones that work. Fluids, more than you think you need if you have a fever. Sleep, in whatever quantity you can get. Simple painkillers from a pharmacy for the aching if you are able to take them, and the pharmacist will tell you which suits you. Steam from a hot shower loosens a blocked nose. Nothing shortens either illness, which is the part nobody wants to hear. If the cough is what bothers you most, our guide to coughs, colds and a fever that will not shift covers that side of it.

When to get urgent help

Both illnesses sort themselves out the overwhelming majority of the time. These are the signs that yours is not going to:

• Breathlessness while you are sitting still, or being unable to finish a sentence
• Chest pain, particularly if it is worse when you breathe in
• Coughing up blood
• Symptoms that were clearly improving and then suddenly got worse again
• A very high temperature that will not come down despite painkillers and fluids
• Confusion, unusual drowsiness, or being difficult to rouse
• Blue or grey lips, face or fingertips
• A rash that does not fade when you press a glass against it

Call 999 for breathlessness at rest, chest pain, blue lips, confusion or a rash that does not fade. For anything urgent that is plainly not an emergency, call 111 at any hour. If you are pregnant, immunosuppressed, or looking after someone frail who has stopped eating and drinking, lower your threshold for picking up the phone.

How an online consultation works for this

A video appointment suits cold and flu questions well, partly because dragging yourself to a waiting room with a fever is miserable for you and unhelpful for everyone sitting in it. You describe how the illness started, how fast, and what your temperature has been doing, and a UK registered doctor works through it with you on camera.

The doctor may prescribe something if it is clinically appropriate, for instance treatment for a bacterial complication, or an antiviral where you are at higher risk and it is early enough to consider. Equally, the outcome may be a clear explanation of why no medicine will help and exactly what to watch for instead, which is useful even though it feels like less. If you need examining in person, the doctor will say so and can write a referral letter. You can check how booking an appointment works and the cost of a consultation in pounds, then get an appointment booked in a couple of minutes.

Two things people get wrong

Green mucus does not mean you need antibiotics. The colour changes as your immune system does its job, and it happens in ordinary viral colds all the time.

Feeling better is not the same as being over it. With flu especially, the fortnight after the fever breaks is when people relapse into exhaustion by going back to a full week of work, childcare and training too soon.

If you have been ill for a few days and you cannot tell whether you are on the normal path or drifting off it, that is precisely the question a doctor can answer quickly. Book a video consultation with a UK registered doctor and get a straight answer about what you have, what will help, and what to keep an eye on.