Normal body temperature is around 36 ° C-37 ° C, but over a single day, it can vary considerably. It is usually somewhat higher in the early afternoon and evening, and lower early in the morning. But…do you know at what temperature fever starts? Let’s take a look.

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What is fever?

Fever is an increase in body temperature. It is a sign and not a disease in itself. It occurs for infinite reasons and is not always due to a serious problem. There are many factors that can affect body temperature, without it meaning you have a serious health issue. For example:

  • Intense emotions.

  • Atmospheric temperature.

  • Physical exercise.

  • A copious meal.

  • Wearing too many clothes.

  • Environmental humidity.

  • Menstrual cycle.

How to take a temperature

Body temperature can be measured with a suitable thermometer either in the armpits, the ears, the rectum or under the tongue, in the mouth. Nowadays there are thermometers that can read your temperature directly from the forehead.

Depending on the part of the body you measure, the temperature may vary a few tenths, although the difference is insignificant when it comes to making a diagnosis.

What temperature indicates fever in children?

According to the Spanish Association of Paediatrics, a fever is considered to be a rectal temperature of over 38°C, or above 37.8°C, if measured in the mouth or armpit. In babies, the reading is more precise when taken from the rectum. The following parameters apply:

  • Low-grade fever: 37.5°C – 38°C.

  • Mild fever: 38.1°C – 38.5°C.

  • Moderate fever: 38.5°C – 39°C.

  • High fever: superior a 39.6°C.

What temperature indicates fever in adults?

Fever is considered to be higher than 37.5°C when measured with the thermometer in the mouth or above 38°C when measured with an axillary thermometer.

Causes of fever

A fever warns us that the body is developing some type of infection or inflammation, generally due to bacteria, viruses or fungi. Hence, myriad occurrences can produce fever. For example, the following commonly result in fever:

Colds, flu, pneumonias, bronchitis, oral or sinus infections, otitis, pharyngitis (aphonia), laryngitis, rhinitis, gastric infections (food poisoning), urinary tract problems (urine infections), childhood diseases, such as rubella, measles, mumps, chicken pox, scarlet fever…traveller’s diseases such as malaria, dengue, haemorrhagic fever…

Benign processes such as hormonal changes, indigestion, heat stroke or, in babies, the eruption of teeth, or being given a vaccine, can also cause fevers.

Other more serious illnesses such as an auto-immune disease, a tumour or sepsis (following a heart attack or burns) are also common causes of elevated temperatures.

Types of fever

  • Continuous fever, when maintained over time with few changes.

  • Remittent fever, which falls, but does not reach normal levels.

  • Intermittent or undulant fever, when it rises and falls and periods of high fever are interspersed with normal temperatures.

Symptoms that accompany fever.

In addition to the symptoms of the underlying illness causing the fever (for example, the flu or a cold), the fever can also be accompanied by:

  • Chills.

  • Sweating.

  • Rapid pulse

  • Rapid shallow breathing.

  • Flushed skin

  • Dry mouth.

  • Dizziness.

  • Loss of appetite

  • Headache

  • Convulsions, confusion, and delirium, when the temperature exceeds 40°C (more common in children).

Fever, as we have said, is just a sign that something is happening, so the doctor should do a complete scan in order to make a differential diagnosis and find out what the underlying cause producing hyperthermia is.

How to lower a fever.

Logically, depending on the underlying cause of the fever one treatment or another will be prescribed. Normally, to reduce high fever, antipyretics are used, many of which also have an analgesic and/ or anti-inflammatory effect, such as paracetamol, ibuprofen or acetylsalicylic acid.

In addition, the doctor will assess the need to administer antibiotics or not depending on which factor is causing the disease.

Natural remedies to treat and reduce fever.

  • Drink plenty of fluids at room temperature.

  • Do not wrap up too much.

  • Avoid excessive ambient temperatures.

  • Rest.

  • Reduce intake of solids.

  • Place wet cloths on your forehead, nape of the neck, wrists or ankles.

  • Avoid an ice bath. It can be counterproductive. Useful, especially in children with a high fever that antipyretics do not manage to reduce, is to give a warm bath or use a soaked sponge to refresh the body.

Fever does not always need to be treated. If it is not due to any major problem and it is not very high, it is possible that the person is well enough to lead a normal life. If drugs are taken without knowing why the fever occurred, you might mask the symptoms of the disease that is producing it. 

Ask your doctor if the fever does not subside within a few hours or is very high and, in children, ask the paediatrician before administering any medication.

If you are an athlete, assess whether it is convenient to take a break until the fever disappears.

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