What is Considered a Fever

A fever is defined as an increase in body temperature above the normal daily range for an individual. The normal body temperature varies depending on age, activity level and time of day. For adults, a fever is generally considered to be a body temperature of 100.4°F (38°C) or higher, while for infants and young children, rectal temperature of 100.4°F (38°C) or higher is considered a fever.

Degrees of Fever

The difference between a fever and “fever of concern” lies in the degree of temperature elevation. A fever is a mild elevation of body temperature, while a fever of concern is a more significant elevation of body temperature.

A fever is typically defined as a body temperature between 100.4°F (38°C) and 102.2°F (39°C), while a fever of concern is generally defined as a body temperature of 102.2°F (39°C) or higher. The exact definitions of each fever category, however,  may vary depending on the individual, age and underlying health conditions. The first level of fever is often a sign of the body’s response to a mild to moderate infection, such as a cold or flu, and may be accompanied by symptoms such as chills, sweating, headache and muscle aches. It is generally not a cause for concern and can be managed with over-the-counter fever-reducing medications, hydration and rest.

In contrast, a fever of concern may indicate a more serious infection or medical condition and should be evaluated by a health care provider. Fever of concern may be accompanied by symptoms such as severe headache, neck stiffness, rapid heart rate, difficulty breathing, lethargy and confusion. Fever of concern accompanied by any of these symptoms may be a sign of a medical emergency, such as sepsis or meningitis, and requires immediate medical attention.

It's important to note that fever is a normal response to infection or inflammation and can help the body fight off infections. Persistent fever or high fever to the level of concern, however, may indicate an underlying medical condition and should be evaluated by a health care provider.

When to See a Doctor Based on Age

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Infants (<3 months)

A rectal temperature of 100.4°F (38°C) or higher is considered a medical emergency and parents should contact a doctor immediately. Rectal temperatures are the most accurate and a reflection of the core temperature, and therefore the recommended method of measurement for all infants. Infants in this age group have immature immune systems and are at extreme risk for serious bacterial infections that can cause fever, such as meningitis, pneumonia, bloodstream infections or urinary tract infections. Infants under 3 months with fever must be seen by a doctor that same day as soon as possible.

Infants (3-6 months)

For infants between 3 and 6 months old, a fever of 100.4°F (38°C) or higher should prompt a call to the child's pediatrician or health care provider. Infants in this age group have immature immune systems and are also at increased risk for serious bacterial infections that can cause fever, such as meningitis, pneumonia or urinary tract infections, in addition to viral infections.

If an infant between 3 and 6 months old has a fever, their pediatrician or health care provider will likely recommend an evaluation in person. During the evaluation, the health care provider may perform a physical exam, take a medical history and order tests such as blood tests or urine tests to determine the underlying cause of the fever.

Infants (6-24 months)

For infants between 6 and 24 months old, a fever of 100.4°F (38°C) or higher that lasts for more than a day or two should prompt a call to the child's pediatrician or health care provider. While fever in this age group is usually caused by a viral infection, such as a cold or flu, it can also be a sign of a bacterial infection that requires treatment.

In addition to fever, parents should also be on the lookout for other signs of illness, such as difficulty breathing, dehydration, vomiting, diarrhea or rash. If an infant is experiencing any of these symptoms in addition to fever, parents should contact their health care provider for advice.

Children

For children, a fever of 100.4°F (38°C) or higher that lasts for more than a day or two should prompt a call to their pediatrician or health care provider. While fever in children is usually caused by a viral infection, such as a cold or flu, it can also be a sign of a bacterial infection that requires treatment.

In addition to fever, parents should also be on the lookout for other signs of illness, such as difficulty breathing, dehydration, vomiting, diarrhea or rash. If a child is experiencing any of these symptoms in addition to fever, parents should contact their health care provider for advice.

If a child is experiencing a fever that is accompanied by other concerning symptoms, such as severe headache, chest pain or difficulty breathing, or has a history of chronic medical conditions, parents should seek medical attention immediately.

Adults

For adults, a fever of 100.4°F (38°C) or higher that lasts for more than a day or two should prompt a call to their health care provider. While fever in adults is usually caused by a viral infection, such as a cold or flu, it can also be a sign of a bacterial infection or other underlying medical condition that requires treatment.

In addition to fever, adults should also be on the lookout for other signs of illness, such as difficulty breathing, chest pain, abdominal pain, severe headache, confusion or rash. If an adult is experiencing any of these symptoms in addition to fever, they should contact their health care provider for advice.

If an adult is experiencing a fever that is accompanied by other concerning symptoms or has a history of chronic medical conditions, they should seek medical attention immediately.

In some cases, health care providers may recommend an in-person evaluation to determine the underlying cause of the fever. During the evaluation, the health care provider may perform a physical exam, take a medical history, and order tests such as blood tests or urine tests to determine the underlying cause of the fever.

Fever in adults can be a serious matter and should be taken seriously. If an adult is showing signs of distress or has other concerning symptoms, such as difficulty breathing or confusion, they should seek medical attention immediately.

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How to Treat a Fever

• Stay hydrated: Drink plenty of fluids, such as water, fruit juice or clear broth to prevent dehydration.

• Rest: Get plenty of rest to help your body fight the infection and conserve energy.

• Reduce body temperature: You can use over-the-counter fever reducers, such as acetaminophen or ibuprofen, to help reduce your fever and relieve symptoms like headache or body aches. You can also take a cool bath or use a cool, damp cloth on your forehead to help lower your body temperature.

• Dress comfortably: Wear lightweight, loose-fitting clothing to help regulate your body temperature.