Is it serious if a child has a high temperature?

Parental concerns owe much to a belief that fever is a disease rather than a symptom

Everybody's got the fever
That is somethin' you all know
Fever isn't such a new thing
Fever started long time ago
– Fever by Peggy Lee, 1958

Although not the original recording, Fever became Peggy Lee's signature song. The jazz/r'n'b number is instantly recognisable by its finger-clicking, exclamatory style.

In the medical world, fever is certainly not a new thing. As far back as Roman times, an unusually high body temperature was seen as a sign of the supernatural. This continued into the Middle Ages, when fever treatments included charms and exorcisms.

Writing in the journal Medical History, Iain Lonie of the Wellcome Trust notes that it was generally agreed by 16th-century writers that the nature of fever lay in the "heat contrary to nature". "Almost all of them regarded this heat as a distinct kind or genus of heat, contrasted with other kinds," he says.


A fever wasn't seen as an extension of a person's body heat, but as some mysterious outside force. "Fever is a mighty engine which nature brings into the world to the conquest of her enemies," wrote the 17th-century English physician Thomas Sydenham.

Despite a greater scientific understanding of the meaning of a high temperature, we retain some of the medieval fear of a fever. It’s especially primal in parents. One of the most common reasons for an out-of-hours call to a doctor is a fever in young children. “When she didn’t respond to paracetamol, I thought it was best to get her seen,” is a frequent consultation opener from a worried parent or guardian.

Described by some researchers as “fever phobia” – an unwarranted concern about a high temperature of up to 39 degrees – I find such labelling a little harsh. Some fevers are slow burn, but some may increase at a fast rate. I’m not sure we should expect any degree of sangfroid among parents of small babies and infants.

What is clear is that our parental concerns around fever owe more to a belief that high temperature is a disease in itself rather than a symptom or sign of illness.


So what does science tell us?

When viruses or bacteria invade, the immune system sends macrophages to attack the invaders. These scavenger cells also let the rest of the body know what’s going on by sending out an alert via proteins called cytokines. They travel to the brain’s pain centre and the hypothalamus – the area of the brain that controls temperature. The hypothalamus responds by initiating a fever.

Perhaps adults shouldn’t be over-treated with fever-reducing drugs until body temperature rises to 39.5 degrees. Illustration: iStock

A higher body temperature makes it harder for bacteria and viruses to thrive and eventually kills them off. White blood cells called lymphocytes also mobilise, with higher body temperatures increasing their effectiveness.

But recent research has opened up another dimension to how fever operates. In a study published in the journal Immunity last month, scientists showed that fever helps more lymphocytes move to the area of the body under attack by a bug. They do this with the help of molecules called integrins, which are attached to the surface of lymphocytes. The researchers found that fever boosts an integrin-supercharging protein called heat shock protein 90 (Hsp90) in white cells. These bind to the integrin tail, two at a time, helping more integrins cluster on the surface of the lymphocyte and move it more efficiently to the area where it's needed most. The researchers found that this doesn't just help T-lymphocytes, but all sorts of immune cells. Interestingly, Hsp90 only kicks in to action at a temperature of 38.5 degrees.

The finding suggests that perhaps we shouldn’t over-treat with fever-reducing drugs. This seems reasonable in adults, at least until body temperature rises to 39.5 degrees.

In children, however, the risk of a febrile convulsion, although probably harmless in the long-term, means earlier intervention is appropriate.

Of course, Peggy Lee is singing about a more adult form of fever.