What is the difference between a cold and a flu?

Immune System Expert
Ask Dr. Jen Tan

14 January 2015

Cold or flu?

What is the difference between the common cold and flu? This is one of the more frequently asked questions on our helpline each winter.

In our minds, a cold is a milder infection which we can fight off easily. On the other hand, flu (short for influenza) might mean that we have to take to our beds, curl up with the hot water bottle and our world stops until we recover.

It would really help if we could tell the difference between a cold and the flu. We would be able to plan our lives better and decisions on whether we need to cancel social engagements and trips would become much easier to make.

What are the similarities?

Firstly, both colds and flu are caused by viruses infecting the upper respiratory system – an area of the body starting from the nose (nasal passages) and sinuses, to the throat (pharynx) and down to the first parts of the tubing which carries air into the lungs (larynx).

More than 200 viruses are known to cause the common cold. These include the viral groups known as coronavirus, RSV (respiratory syncytial virus) and rhinovirus.

In contrast, flu is caused by just one type of virus known as the influenza virus. This group is divided into 3 main sub-types known as influenza A, B and C.

So, whether you have the common cold or flu simply comes down to the type of virus infecting your body! Simple.

Influenza is a more serious illness than colds

It is a common perception that flu gives rise to more severe symptoms than colds. In general, this is correct.

Each winter, flu is known to be a factor in the early death of those in poor health and vulnerable, such as the elderly and people with chronic illnesses. And, of course, we have all heard of swine flu and bird flu which are serious health conditions.

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How can we tell the difference between colds and flu?

It has been estimated that each of us is subject to an average of between 2 and 4 viral infections a year. So, colds and flu are very, very common and for the vast majority of us, these infections are relatively minor health inconveniences.

Whilst it is true that influenza is a more serious infection, it is actually very difficult to tell the difference between an infection caused by the flu virus and an infection arising from one of the 200 or more common cold viruses, based on symptoms alone.

For instance, if we have a sore throat, a blocked nose or feel a bit tired, we might say that we are coming down with the cold. If additional symptoms develop such as feeling achy in our muscles and joints, loss of appetite or feeling feverish and needing to take to our beds, we would say that we have picked up the flu.

You would have thought that going to your doctor would make it clearer whether you are suffering from the cold or flu. However, this is not the case. Doctors are not able to accurately tell the difference whether it is the common cold or flu virus causing you problems based solely on the severity of symptoms. What is thought to be a flu because of severe symptoms can be a cold and vice versa. The only way to be sure is to do some viral tests involving taking a swab from the back of the throat and sending the sample to the laboratory.

Does it matter?

So, it is clear that trying to tell the difference between a cold or the flu, based simply on how you are feeling, is very difficult. The only accurate way of obtaining the answer is to use a laboratory based test to identify the type of virus infecting your body.

One reason why doctors would want a clear diagnosis is to help them make the decision on whether or not it is appropriate to prescribe a synthetic anti-viral drug for flu such as Tamiflu. However, laboratory test results take a few days to come through and treatment should be started as soon as possible to be effective.

So, at the moment, decisions are still mainly made based on symptoms – sometimes the decision is right; sometimes, it is wrong.

Apart from the scientific reasons for knowing what sort of infection you have, there is one practical purpose for knowing the difference between a cold and the flu. If you are really suffering from flu, you will want to know if the infection is likely to keep you at home for a few days so that you can tell those at work and re-arrange the diary.

Why it does NOT matter

Although colds and flu are scientifically different illnesses, the way we would handle them will be the same. In practice, we will just listen to what our body is telling us. After all, some infections caused by common cold viruses can cause more severe symptoms than those caused by the influenza virus.

If telling one virus from the other involves tests which take time, does it really matter for you to know which type of virus you have? You should have recovered by the time the results are in your letterbox.

How to handle colds & flu

  1. If you are feeling lousy, stay at home and give yourself the best chance of getting back to your usual perky self as quickly as possible. This is much preferable to infecting your colleagues and friends
  2. If however, you only suffer mild symptoms, whether due to the common cold or flu virus, you might find that you can keep going with your normal routine. And, there is no reason why not. This is, after all, what we have all been doing all these years
  3. And, if you were treating yourself with Echinacea, it does not matter which type of virus you have as this herb has been shown to help with both the common cold and influenza viruses
  4. Whether it is the cold or the flu, keep yourself hydrated – any type of fluid will do but plain ordinary water is best. Don’t worry if you don’t feel like eating for a day or so – it is the body being sensible.
  5. And lastly, don’t feel guilty about retreating to your bed, taking a few days off work and telling your friends that you can’t see them. If you are feeling really ill, have a high temperature and are worried about your health, call your doctor.

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