Fever: what it is, causes, types (and what to do)

Fever is when body temperature is above 38ºC, being a natural defense mechanism of the body, which makes it difficult to develop most microorganisms, helping the immune system to combat infections. For this reason, fever is a very little specific symptom, as it can have several causes, from flu, tonsillitis, covid-19, autoimmune diseases and even cancer, for example.

Although the value of 38ºC is used to define fever, the truth is that fever is any elevation of temperature above the normal range for each person. This is why some people may feel “feverish” and with general discomfort even when the temperature is still close to 37.5ºC.

Also read: Fever that comes and back: 9 Possible causes (and what to do)

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Whenever fever is too high (over 40ºC) or persists for more than 3 days, it is important to consult a general practitioner to identify the cause and start the most appropriate treatment.

How to know if it is fever

If you think it may have a fever, please indicate its temperature value in the calculator:

Understand better than temperature is fever and when to worry.

Fever symptoms

The main symptoms of fever are:

• Body temperature equal to or greater than 38ºC;
• Hot and dry skin;
• Chills;
• Redness on the face;
• Cold sweat;
• Tiredness or general malaise.

In addition, fever may be accompanied by other symptoms such as nausea, diarrhea, loss of appetite, decreased amount of urine or headache, muscle or sore throat, for example.

Main causes of fever

The main causes of fever are:

1. Infections

Infections by viruses, bacteria or parasites are the main cause of fever. The most common include:

• Pneumonia;
• Gripe;
• Sinusitis;
• COVID-19;
• Malaria;
• For.

In addition to fever, it is common for other symptoms to appear and respiratory changes, headache, malaise, excessive tiredness or weakness may arise according to the type of infection.

What to do: It is important to consult a general practitioner to do tests that help identify the infectious agent and thus start the most appropriate treatment that may involve the use of antibiotics or antivirals. In addition, it may be recommended to be resting.

2. Autoimmune diseases

Some autoimmune diseases, such as rheumatoid arthritis and Crohn’s disease, can also cause high and persistent fever.

This is because healthy body cells are being attacked, leading to the development of chronic inflammation, which results in increased body temperature.

In the case of rheumatoid arthritis, in addition to fever, it is also common to have joint pain and stiffness, redness and difficulty moving the affected joint.

In the case of Crohn’s disease, other symptoms besides fever are intense diarrhea, abdominal cramps and weight loss, for example.

What to do: It is important that the doctor’s guidelines are followed, which usually indicate the use of medicines that decrease the activity of the immune system, promoting symptom control.

In addition, anti-inflammatory drugs or corticosteroids may be recommended to relieve symptoms. In the case of Crohn’s disease, it is essential that the person also has the guidance of a nutritionist, to make a diet that prevents crises. See what the food for Crohn’s disease should be.

Also read: Rheumatic fever: what it is, symptoms, causes and treatment

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3. Vaccines

Some vaccines may have an adverse reaction to fever. This happens mainly in vaccines that are manufactured with an attenuated form of the infectious agent or toxin, which makes the immune system produce antibodies that, in addition to stimulating immunity, can also produce fever.

Some of the vaccines that have a side effect to fever are: the antiteanic vaccine, the diphtheria vaccine and covid-19 vaccines, for example.

What to do: Fever is considered normal after vaccination, disappearing after a few hours without having any treatment.

However, to relieve fever, you can take a warm bath, stay in a ventilated environment and put a wet towel with cold water on your forehead and fists, for example. See more ways to download fever.

4. Use of medicines

Some medications such as antimicrobial, antihistamines, antidepressants, opioids, antiemetics and central nervous system stimulants, for example, may also have a side effect to fever.

What to do: If it is suspected that the fever is caused by the use of any medicine, it is important to inform the doctor in order to evaluate the need to exchange or suspend the use of the drug.

5. Cancer

Fever may be present in some types of cancer, especially in the most advanced stages, where other organs are hit by tumor cells. Check out the symptoms that may indicate cancer.

What to do: It is important to inform the physician of the symptom presented and follow the recommended treatment. In some cases, cancer treatment may be required to prevent further progression of the disease.

6. Arboviruses

Arboviroses, such as dengue, chikungunya, zika, yellow fever or oropouche fever, can also cause high fever, besides headache, joint pain, pain behind the eyes, nausea, vomiting, red spots and itching on the skin.

What to do: The general practitioner should be consulting, to be evaluated the symptoms and tests that help differentiate arboviruses and then can start the most appropriate treatment, which usually involves rest and good hydration. See how to know if it is dengue, zika and chikungunya.

In some cases, the doctor may recommend the use of painkillers, such as dipyrone or acetaminophen to relieve symptoms. Under no circumstances, anti-inflammatory drugs should be used as they are contraindicated in cases of suspected or confirmed dengue.

Also read: Hemorrhagic fever: what is, symptoms, causes and treatment

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How to measure at body temperature

To know the body temperature and confirm the fever, it is recommended to make use of a thermometer: digital or glass (which should be placed in the armpit, mouth or anus) or infrared (which just be pointed to the forehead).

Also read: How many degrees is fever (and how to measure temperature)

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Fever types

The main types of fever are:

1. High fever

High fever is when the measured temperature with axillary thermometer is greater than 39ºC.

This type of fever can be caused by infections, insolation, sepsis, meningitis, intracranial hemorrhage, Mayaro fever, foot -and -mouth disease, typhoid fever, malignant neuroleptic syndrome or spotted fever, for example.

Also read: Football Fever: What is, Symptoms, Transmission and Treatment

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2. Fever of indeterminate origin

The fever of indeterminate origin, also called the fever of unknown origin, is a type of fever in which the cause was not discovered by diagnostic tests, being characterized by axillary temperature greater than or equal to 38.3 ° C.

Also read: Fever without symptoms: what can be (and what to do)

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3. Sudden fever

Sudden fever is one that suddenly arises, which may happen due to infections such as covid-19, flu, urinary tract infection or gastroenteritis, for example.

4. Persistent fever

Persistent fever is a type of fever that does not improve and is usually caused by chronic infections such as tuberculosis, HIV, Epstein-Barr virus, for example.

In addition, persistent fever can also be caused by cancer or autoimmune diseases.

Also read: Nile fever: what is, symptoms and treatment

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5. Low fever

Low fever, also called fever or feverish state, is characterized by an axillary temperature of between 37.3 and 37.8ºC, caused by flu, colds, pneumonia or sinusitis, for example.

This type of fever can also appear in babies with the birth of the teeth and usually lasts from 1 to 2 days. However, if the baby has a high fever, it should always be taken to the pediatrician to identify the cause.

Also read: Baby fever: How many degrees, causes and what to do

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6. Internal fever

Internal fever is a popular expression used for the sensation of hot body, but body temperature remains normal, between 36 to 37ºC.

However, in these cases, the person may have symptoms of fever, such as malaphy, chills or tiredness. Learn more about internal fever.

7. Emotional fever

Emotional fever, or psychogenic fever, is a type of fever caused by stress, anxiety or mental disorders, causing the body temperature to increase and can reach up to 40 ° C. Understand better what it is and causes of emotional fever.

8. Night fever

Night fever is a type of fever that appears only at night and can be caused by infections, cancer or autoimmune diseases, for example.

9. Fever that comes and go

The fever that comes and back, also known as intermittent fever, is a type of fever that appears a few hours of the day, improves and then returns.

This type of fever because it is caused by infections such as zika, tuberculosis, leptospirosis or cancer such as lymphoma, for example. See other causes of the fever that comes and back.

How to relieve fever

To relieve fever, it is recommended:

• Rest, avoiding efforts to help the immune system combat infections;
• Increase fluid consumption such as water, teas or soups to avoid dehydration. See some teas to download fever;
• Remove excess clothing and covered except if the person has chills;
• Take a warm bath;
• Place a wet towel in cold water on the forehead and wrists.

In addition, antipyretic remedies such as acetaminophen, dipyrone or ibuprofen can be taken. Ibuprofen and other anti-inflammatory drugs should not be taken in the case of suspected or confirmed dengue. Check out the main remedies for fever.

Also read: How to download baby fever (and when worrying)

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Watch the following video with tips on how to relieve fever: