Having a fever means that your body temperature is higher than normal. Something inside your body, such as an infection, has caused your temperature to go up. A basic fever, one due to minor bacterial or viral illness, can be an expression of the immune system working at its best.
A part of the brain called the hypothalamus controls your body temperature.
Normally, the hypothalamus keeps your temperature at around 37ºC (98.6ºF). This can vary depending on the time of day – your temperature is usually lowest in the early hours of the morning and highest in mid afternoon. But generally, it stays around 36.5 and 37ºC.
When you have a fever, your body temperature rises above 38ºC (100.4ºF). This usually means there is something wrong somewhere.
The 3 phases of fever
Even though having a fever is uncomfortable, it is not a bad thing. It is your body’s way of letting you know something is wrong. In a way, the fever is helping to fight off your infection. This happens in 3 phases
- Your body reacts and heats up
- The fever levels off
- Cooling down
Your blood and lymphatic system makes white blood cells, which fight infection. When you have an infection you make lots and lots of these cells. They work faster and faster to try and fight off the infection. The increase in these white blood cells affects the part of your brain that controls your body temperature (the hypothalamus). This makes your body heat up, causing a fever. Fever also impairs the replication of many bacteria and viruses.
In the early stages of a fever you often feel cold and start to shiver. This is your body’s response to a rising temperature – the blood vessels in your skin tighten up (constrict), forcing blood from the outer layer of your skin to inside your body where it is easier to keep the heat in. The outer skin layer then becomes cool and your muscles start to contract. This makes you shiver. Shivering produces more heat and raises your temperature even more.
In the second phase of a fever, the amount of heat you make and lose is the same. So the shivering stops and your body remains at its new high temperature.
Your body starts to try and cool down so that your temperature can return to normal. The blood vessels in the skin open again, so blood moves back to these areas. You may sweat, as this helps to cool down the body.
This phase of a fever may or may not happen naturally. You may need to have some medication to start it off, as well as treating the underlying cause of the fever.
Treatment of fever
Fever should not necessarily be treated. Fever is an important signal that there’s something wrong in the body, and it can be used to govern medical treatment and gauge its effectiveness. Moreover, not all fevers are of infectious origin.
Treatment of fever is normally done by lowering the set-point, but facilitating heat loss may also be effective.
The former is accomplished with antipyretics such as ibuprofen or acetominophen (aspirin can be given to adults, but can cause Reye’s Syndrome in children). Antipyretics cause the hypothalamus to override the induced increase in temperature. The body will then work to lower the temperature and the result is a reduction in fever.
Heat removal is generally by wet cloth or pads, usually applied to the forehead. Heat loss may also be accomplished by evaporation (sweating, perspiration). This is particularly important for babies, where drugs should be avoided.
Who is most at risk of having complications from a fever?
The very young and elderly are more likely to get complications from a fever.
In the elderly, the part of the brain that regulates temperature (the hypothalamus) does not work as well as it does in the young. The body temperature can rise too much, causing heart problems and confusion.
Children under six may have a fit (seizure) if their temperature gets too high.
But in most people, the cause of the fever – such as infection – is more likely to cause problems than the fever itself and the body does its best in repairing itself.
Fever is only a symptom, not a disease, most often scary and annoying, but in most cases not dangerous.