Fever, quite simply, is an increase in body temperature that’s usually a protective response to an infection caused by a virus or bacteria. The raised body temperature enhances the body’s defence against the infection, but may cause some discomfort.

Body temperature is regarded as raised when it’s above 38 degrees Celsius as measured by an oral thermometer. Although 37 degrees Celsius is considered to be a normal temperature, this varies throughout the day, being lowest in the morning and highest in the late afternoon.

Fever results from a re-setting of the body’s thermostat. Body temperature rises in response to blood moving from the surface to the interior of the body, thus reducing heat loss. Shivering or chills may occur to increase heat production through contraction of muscles.

The body’s effort to conserve heat continues until blood reaches the hypothalamus (the part of the brain that controls body temperature) at the new, higher temperature, which is then maintained.

Later, when the thermostat is re-set back to its normal level, the body eliminates excess heat through sweating and shunting blood to the skin.

Causes of fever

Fever can be caused by factors outside or inside the body. Bacteria and viruses can produce chemical poisons, which may cause white blood cells to release pyrogens. It’s the pyrogens that actually cause the fever.

Pyrogens are produced in response to infection, inflammation, cancer, allergies and in immune diseases such as rheumatoid arthritis. Over-exercising in hot weather, over-exposure to sunlight or some medications can cause a very high fever at times, sometimes requiring urgent medical care.

Fever ranges and symptoms

The best way to take your temperature is to use a digital thermometer placed under the tongue for 2-3 minutes.

Mild fever  (38-39?C)

With a mild fever, you may have flushed cheeks, feel unwell and be warm to the touch. You should, however, be able to carry on with normal daily activities.

High fever (39?C)

With a high fever, you’ll not feel well enough to go to work; you may have a headache and aches and pains in your legs and muscles. You will feel hot to the touch.

Very high fever (40?C or higher)

With a very high fever, you’ll need to stay in bed. You won’t be well enough to carry out normal activities. You may lose your appetite and you’ll feel very hot to the touch.

When to see a doctor

In most cases, fever can be managed without seeing a doctor. When deciding whether to go to the doctor or not, it’s always best to take all of your symptoms into account.

It’s always necessary to see the doctor if you:

    • Have a very high fever of 40 degrees Celsius or higher.

    • Have pain elsewhere in the body, such as in your ears, sinuses, chest or abdomen.

    • Haven’t had anything to drink for several hours and you’re constantly vomiting.

    • Find that bright light hurts your eyes.

    • Have a rash, especially red or purple spots anywhere on your body.

    • Are no better after 48 hours.

    • Have difficulty waking up or feel drowsy.

    • Feel increasingly ill.

    • Have visited a tropical country or a country where malaria is prevalent.

    • Have blood in your stool.

    • Have a very painful throat.

    • Have a swollen, hot or red skin (even if it’s just in one area of your skin).

How to treat a fever

Self-care at home

Take your temperature with a digital thermometer placed under your tongue for 2 to 3 minutes.

If your temperature is 40 degrees Celsius or higher you must see a doctor.

However, if you have a mild to moderate fever (38-38.9?C), ibuprofen or paracetomol could help to break it. Both these medications also help to control pain. Alternating doses of each will also help and will prevent accidental overdose of one of the medicines. At times a combination of both paracetomol and ibuprofen will be needed to stop the fever.

Note that aspirin isn’t a first-choice treatment for fever reduction. In fact, it should never be used in children or anyone under the age of 18 years. Aspirin may be toxic in large doses in adults or cause a severe illness called Reye’s syndrome in children.

Cool, wet towels applied to the skin will also help to reduce fever. Drink as much fluid as possible, especially water, as this helps maintain hydration and will also help to cool you down.

If the fever is caused by over exposure to hot weather or over-exertion, this may result in a condition called heat stroke or heat exhaustion. It’s important to seek medical help immediately.

Follow up

Most fevers will go away in a few days with the correct treatment. If symptoms worsen or if the fever lasts for more than three days with treatment, visit your doctor immediately.

Following up with your doctor is important, especially if the fever is due to cancer, allergic reactions to medicines, where an unusual infection is the cause, or where the fever is persistent and the cause isn’t obvious.

Some people may experience relapses and develop fever again and require further treatment. In some cases it may be necessary to be admitted to hospital for special tests to find out the cause of a recurring or persistent fever.

Image via Thinkstock