What does it mean to have a fever?
What does it mean to have a fever?
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Having a fever means that your body temperature has temporarily increased and it is a signal that your body may be fighting off an infection. The U.S. Centers for Disease Control define a fever as a measured temperature of at least 100.4°F (38°C), slightly higher than the average human temperature of 98.6°F (37°C). Fevers are one of the immune system's first reactions to a pathogen - such as a virus or bacteria entering the body. Fevers can also be caused by environmental factors like heat stroke or biological responses like alcohol withdrawal. Your body senses these potential threats and forces itself to raise its temperature (by creating a fever, through chemicals in your blood called 'pyrogens') to make it difficult for the pathogen to use your body as a host and reproduce viruses or bacteria. Normal body temperatures change every day and usually vary between 97.6°F (36.4°C) and 99.6 °F (37.5°C) with lower body temperatures generally occurring in the morning and higher temperatures occurring at night. For most adults, short-term fevers shouldn't be alarming unless it reaches 103°F (39.4°C) or higher. For infants younger than 3 months, a rectal temperature of 100.4°F (38°C) or higher signals a fever and in that case a doctor should be contacted. For infants between 3 - 24 months, a rectal temperature of 102°F (38.9°C) signals a fever that should also be discussed with a doctor. For other young children, even slight fevers can signal infections, so a doctor should be consulted if a fever appears.
Having a fever means that your body temperature has temporarily increased and it is a signal that your body may be fighting off an infection. The U.S. Centers for Disease Control define a fever as a measured temperature of at least 100.4°F (38°C), slightly higher than the average human temperature of 98.6°F (37°C). Fevers are one of the immune system's first reactions to a pathogen - such as a virus or bacteria entering the body. Fevers can also be caused by environmental factors like heat stroke or biological responses like alcohol withdrawal. Your body senses these potential threats and forces itself to raise its temperature (by creating a fever, through chemicals in your blood called 'pyrogens') to make it difficult for the pathogen to use your body as a host and reproduce viruses or bacteria. Normal body temperatures change every day and usually vary between 97.6°F (36.4°C) and 99.6 °F (37.5°C) with lower body temperatures generally occurring in the morning and higher temperatures occurring at night. For most adults, short-term fevers shouldn't be alarming unless it reaches 103°F (39.4°C) or higher. For infants younger than 3 months, a rectal temperature of 100.4°F (38°C) or higher signals a fever and in that case a doctor should be contacted. For infants between 3 - 24 months, a rectal temperature of 102°F (38.9°C) signals a fever that should also be discussed with a doctor. For other young children, even slight fevers can signal infections, so a doctor should be consulted if a fever appears.
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What our experts say
Having a fever means that your body temperature has temporarily increased and it is a signal that your body may be fighting off an infection. The U.S. Centers for Disease Control define a fever as a measured temperature of at least 100.4°F (38°C), slightly higher than the average human temperature of 98.6°F (37°C). Fevers are one of the immune system's first reactions to a pathogen - such as a virus or bacteria entering the body. Fevers can also be caused by environmental factors like heat stroke or biological responses like alcohol withdrawal. Your body senses these potential threats and forces itself to raise its temperature (by creating a fever, through chemicals in your blood called 'pyrogens') to make it difficult for the pathogen to use your body as a host and reproduce viruses or bacteria.
Normal body temperatures change every day and usually vary between 97.6°F (36.4°C) and 99.6 °F (37.5°C) with lower body temperatures generally occurring in the morning and higher temperatures occurring at night. For most adults, short-term fevers shouldn't be alarming unless it reaches 103°F (39.4°C) or higher. For infants younger than 3 months, a rectal temperature of 100.4°F (38°C) or higher signals a fever and in that case a doctor should be contacted. For infants between 3 - 24 months, a rectal temperature of 102°F (38.9°C) signals a fever that should also be discussed with a doctor. For other young children, even slight fevers can signal infections, so a doctor should be consulted if a fever appears.
Having a fever means that your body temperature has temporarily increased and it is a signal that your body may be fighting off an infection. The U.S. Centers for Disease Control define a fever as a measured temperature of at least 100.4°F (38°C), slightly higher than the average human temperature of 98.6°F (37°C). Fevers are one of the immune system's first reactions to a pathogen - such as a virus or bacteria entering the body. Fevers can also be caused by environmental factors like heat stroke or biological responses like alcohol withdrawal. Your body senses these potential threats and forces itself to raise its temperature (by creating a fever, through chemicals in your blood called 'pyrogens') to make it difficult for the pathogen to use your body as a host and reproduce viruses or bacteria.
Normal body temperatures change every day and usually vary between 97.6°F (36.4°C) and 99.6 °F (37.5°C) with lower body temperatures generally occurring in the morning and higher temperatures occurring at night. For most adults, short-term fevers shouldn't be alarming unless it reaches 103°F (39.4°C) or higher. For infants younger than 3 months, a rectal temperature of 100.4°F (38°C) or higher signals a fever and in that case a doctor should be contacted. For infants between 3 - 24 months, a rectal temperature of 102°F (38.9°C) signals a fever that should also be discussed with a doctor. For other young children, even slight fevers can signal infections, so a doctor should be consulted if a fever appears.
Context and background
Fever has emerged as a common symptom of COVID-19 infection. A World Health Organization report from February of 2020 suggested that fever was reported in 87.9% of patients with confirmed COVID-19. Fever is an increase in body temperature that is a common symptom of illness or infection, but there are other possible reasons for fever that include heat exhaustion, some medications or immunizations, certain types of cancers, and some inflammatory conditions (i.e. rheumatoid arthritis).
While the average normal temperature is 98.6°F (37°C), there is some individual variation where an individual’s normal temperature may be slightly higher or lower even when he or she is healthy. In addition, normal body temperature can vary during the day and is often lower in the morning and higher later in the day. A normal temperature range is generally about 97°F (36.1°C) to 99°F (37.2°C).
Fever has emerged as a common symptom of COVID-19 infection. A World Health Organization report from February of 2020 suggested that fever was reported in 87.9% of patients with confirmed COVID-19. Fever is an increase in body temperature that is a common symptom of illness or infection, but there are other possible reasons for fever that include heat exhaustion, some medications or immunizations, certain types of cancers, and some inflammatory conditions (i.e. rheumatoid arthritis).
While the average normal temperature is 98.6°F (37°C), there is some individual variation where an individual’s normal temperature may be slightly higher or lower even when he or she is healthy. In addition, normal body temperature can vary during the day and is often lower in the morning and higher later in the day. A normal temperature range is generally about 97°F (36.1°C) to 99°F (37.2°C).
Resources
- CDC Definition of Signs, Symptoms, and Conditions of Ill Travelers (U.S. CDC)
- An article about fever and the immune system (NIH/NCBI)
- An article about fevers promoting T lymphocyte trafficking (Cell)
- Report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19) (WHO)
- Fever (Mayo Clinic)
- CDC Definition of Signs, Symptoms, and Conditions of Ill Travelers (U.S. CDC)
- An article about fever and the immune system (NIH/NCBI)
- An article about fevers promoting T lymphocyte trafficking (Cell)
- Report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19) (WHO)
- Fever (Mayo Clinic)
