24 September 2020

Key points

  • A fever is the body’s defence mechanism — a warning that something is wrong and worth investigating. Many illnesses cause one: the common cold, influenza, COVID-19, and meningitis among them.
  • You cannot tell which illness it is from the fever alone, nor how serious it is from how high the fever runs. That has to come from the other signs and symptoms.
  • A normal temperature is traditionally given as 37°C, but it differs from person to person and changes with the time of day, how much you are wearing, and what you were doing when you measured it. 37 is only a number; normal is really a range.
  • The definition of fever is 0.5°C (1°F) above your own normal temperature — and it is the same for children as for adults.
  • There are two kinds of measurement. Core temperature: traditionally oral or rectal, now usually the ear, which is accurate when done properly. Surface temperature: forehead or underarm. The forehead has a wide margin of error and suits screening only. For babies under 6 months the underarm is a reasonable choice, since oral or rectal readings are awkward or risky in a very small baby, and held in place long enough — a minute to a minute and a half — the underarm reading is accurate.
  • A tip for parents: take your child’s temperature while they are well, using whatever method you normally use at home, to establish their own normal — say 36.8 to 37.3. Then when they are unwell you know that 37.8 counts as a fever.
  • The idea that a fever makes a child grow taller has no basis in science or medicine. Two things may explain the belief. Standing upright, gravity slightly compresses the cartilage between the vertebrae; a sick child lying in bed loses that compression, and on getting up may measure about a centimetre taller. The other explanation runs the other way round: growth can cause mild inflammation in the joints, which brings on a slight fever — so growing causes the fever, not the other way about.
  • Illnesses that bring on fever, such as influenza and meningitis, can be prevented by vaccination, which makes vaccination important — especially the first three infant doses at two, four and six months, which are best not delayed by long. Even when parents are wary of taking a child out, some clinics offer a doctor or nurse who will come to the home to vaccinate.