October 01, 2020 3 min read

With a fever reported to be the most common symptom of COVID-19, the above is a very pertinent question. Yes, you’ll be aware already that the term ‘fever’ refers to an elevated body temperature – but what temperature actually constitutes a fever, and how concerned should you be by it?

Assessing whether you do, or don’t, have a fever

First of all, it’s important to know what represents a ‘normal’ body temperature... which turns out to be different for everyone, not even staying the same over the course of the day.

As the NHS outlines, a high temperature – or fever – is generally considered to be 38 degrees C or more. However, while it’s possible to take your temperature using a digital thermometer from a supermarket or pharmacy, it isn’t always easy to achieve an accurate reading. So, the result you get at a given time might not reflect whether you genuinely do have a fever.

In any case, you don’t always need to take your temperature to be fairly sure that you have a fever – your chest or back simply feeling hotter than usual may be a strong enough indication.

Understanding what a fever is... and what it isn’t

The good news is that fevers are generally not dangerous. From the point of view of the sufferer, they are usually just a reflection that something out of the ordinary is occurring in their body – often an infection that their immune system is trying to fight.

Various studies down the years have given us greater insight into exactly what happens in our bodies when we suffer from a fever. It turns out that a fever is not a mere by-product of our immune response, but is actually fundamental to it, with higher body temperatures spurring cellular mechanisms into action to tackle the viral or bacterial threat.

Mathematicians and biologists from Warwick and Manchester Universities have previously observed that small increases in temperature speed up a cellular ‘clock’ that controls the body’s response to infections.

Meanwhile, researchers at the Shanghai Institute of Biochemistry and Cell Biology in China conducted experiments in mice which showed that when body temperature increases, immune cells known as T cells begin to produce heat-shock proteins (Hsps) to protect cells against stress.   

When does a fever become dangerous?

Fevers are generally a good thing for your health in that they represent your body raising the temperature in an effort to make life inhospitable for germs that might otherwise multiply.

If, however, a fever becomes too high, there might be a risk of it harming you. High-grade fever is known as hyperpyrexia, and is defined by temperatures of more than 103 degrees Fahrenheit, or about 39.4 degrees Celsius.

But given the aforementioned variances in body temperature explained above, it’s important not to necessarily become too hung up on a particular temperature reading. In any case, while many people worry about an especially high and prolonged fever potentially causing brain damage, the reality is that this is an extremely rare event.

Instead, then, you are generally advised to follow the NHS’s broad advice on treating a fever, including getting lots of rest, drinking plentiful fluids and taking paracetamol or ibuprofen in case of discomfort. If this describes your situation right now, we wish you a swift and full recovery!

Other sources:

https://www.mayoclinic.org/diseases-conditions/fever/symptoms-causes/syc-20352759

https://www.healthline.com/health/what-is-normal-body-temperature

https://www.healthline.com/health/cold-flu/fever-in-adults