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How to know when you have a fever

The safest way to know if you have a fever is to use a thermometer to measure your temperature, therefore you should not rely on just placing your hand on the forehead or the neck, for example.

When using a mercury thermometer, which is the most common type, you should consider that there is a fever when the temperature in the armpit is over 37.8°C, since 37.5°C is easily reached when it is very hot or a person has many layers of clothing.

In cases where the temperature is higher than 39°C, it is recommended to go to the emergency room immediately, as high fever can lead to convulsions or endanger the person's life.

 How to know when you have a fever

How to measure body temperature

To measure body temperature you can use:

  • Mercury thermometer: just place the metallic tip in the armpit, in direct contact with the skin and wait at least 3 minutes to check for fever;
  • Digital thermometer: Aim the tip of the thermometer to the forehead or into the ear, after the beep it will show the temperature;
  • Soft-tip thermometer: Insert the metal tip into the baby's or an infant's anus while they are still and wait at least 3 minutes to check for fever.

The best thermometer is the soft-tip because it can be inserted into the anus, this being the correct body temperature, since the skin cools faster. The variation can reach 1ºC.

In an adult, what temperature is considered a fever?

The normal body temperature varies between 35.4ºC and 37.2ºC, however, it can vary in situations of influenza or infection, such as pneumonia, for example. The main variations in body temperature include:

  • Slightly high temperature: between 37.4ºC and 38ºC. In these cases, usually other symptoms appear, such as chills, tremors or redness of the face and the first layer of clothing should be removed, take a  warm water bath or drink water;
  • Fever: temperature above 38.1°C. In adults, it is recommended to take a 1000 mg Paracetamol tablet, to maintain only one layer of clothing and to put cold patches on the forehead. If the temperature does not decrease after 3 hours, go to the ER;
  • Low body temperature (hypothermia): less than 35.4°C, usually occurring when a person is exposed to the cold for a long time. In these cases, one should try to dress several layers of clothes, drink hot tea or warm the house, for example.

In addition, your temperature may also be lower than normal, for example less than 35.4 ° C. This usually happens when you are exposed to the cold for a long time. In these cases, you should try to remove the source of the cold and wear several layers of clothing, drink hot tea or warm the house, for example.

How to measure fever in a baby

The body temperature in a baby should be measured with a thermometer, just like an adult, but it's preferable and more comfortable to use fast thermometers, such as digital or infrared.

However, the ideal place to assess your baby's temperature is the anus, and in these cases you should use the soft-tipped digital thermometer so you do not hurt your baby.

 How to know when you have a fever

In a baby, what temperature is considered a fever?

A baby's body temperature  is different from an adult, so there normal temperature is between 36ºC and 37ºC, and the temperature showed on the thermometer should be evaluated as follows:

  • High temperature: between 37.1ºC and 37.5ºC. In these cases, one should remove a layer of baby's clothing and give a warm water bath;
  • Fever: anal temperature above 37.8°C. In these cases, parents should consult their pediatrician to advise the use of fever medication or the need to take the baby to the emergency room;
  • Low body temperature (hypothermia): less than 35.5ºC. In these cases, one should dress another layer of clothing to the baby and avoid drafts. If the temperature does not increase in the next 30 minutes, the baby should be taken to the emergency room.

Variations in the baby's temperature may not always be due to illness or infection, and may be because of the amount of clothing worn, the birth of teeth, reaction to a vaccine or due to the environment temperature, for example.

Find out how to identify the cause of a baby's fever and how to lower it naturally.

When to take medication to lower a fever

Removing excess clothing and taking a warm shower is a good way to lower body temperature, but when that is not enough, your doctor may recommend taking an antipyretic to lower the fever. The most indicated medication is Paracetamol, which can be taken up to 3 times a day. See other medications to lower a fever.

When should you measure the temperature

Body temperature should be measured when a person is resting and never immediately after physical activity or after a bath because the value may not be real. Therefore, in these cases, you should rest in a cool and airy place for about 15 to 30 minutes before using the thermometer.

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