What Is a Fever?

A fever occurs when your hypothalamus, the thermoregulatory center, adjusts the set point of your normal body temperature upward in response to an infection. Also known as pyrexia, a fever is an expected and important element of your body’s immune system.

An elevated body temperature facilitates a series of mechanisms that help regulate your body’s natural defenses. This ensures that your immune system takes the necessary action against offending infections.

For this reason, a fever is a common side effect of getting a vaccination. The purpose of a vaccination is to jumpstart your immune system into fending off infections. A strong immune response can cause a fever.

Many medical conditions, both infectious and non-infectious, can cause a fever. Fevers can come and go without treatment, but sometimes they indicate a more serious problem, such as a cold or the flu.

Note that allergies do not cause fevers, as noted by the American College of Allergy, Asthma and Immunology. This is a common misconception.

In some instances, allergies can lead to medical conditions that do trigger a fever, such as sinusitis. People who have asthma or allergic rhinitis have an increased risk of developing a sinus infection, which can bring allergy symptoms along with a fever.

A fever is a beneficial natural defense response, and most fevers abate with home care or as they run their course. However, sometimes a fever can be a sign of a serious medical condition that requires medical attention.

A long-lasting high-grade fever with a body temperature above 103 degrees F (39 degrees C) or a fever that doesn’t respond to treatment can lead to complications, including febrile seizures, brain damage and even death.

Febrile seizures, also known as febrile convulsions, are brief convulsions that can occur when a child has a temperature of 100.4 degrees F (38 degrees C) or higher. Febrile seizures often affect children between the ages of six months and 3 years. While they are sometimes frightening, febrile seizures are usually harmless, with nearly all children making complete recoveries.

In rare cases, brain damage may occur when a fever rises above 107.6 degrees F (42 degrees C). Fortunately, untreated fevers will rarely go above 105 degrees (41 degrees C). Prolonged high fevers can also damage the heart and cardiovascular system as well as the liver and kidneys. They may even cause death.

How you care for a fever depends on its severity. Professional medical treatment is not usually required, especially for a low-grade fever. If you have a fever and generally feel fine, there is no emergency and no need to call a doctor or urgent-care facility.

In fact, a growing school of thought is not to treat all fevers. Because a fever helps fight infection, treating it can interfere with this process.

Nonetheless, drinking plenty of fluids and getting enough bed rest is often sufficient to break a fever. You can also take over-the-counter antipyretics such as ibuprofen and acetaminophen.

You can treat elevated body temperature by ensuring the room where you are resting is comfortable. It should be cool (but not cold) and well ventilated.

You may benefit from a cold compress on your forehead. You can also take regular baths with lukewarm water to cool off. However, doctors do not advise bathing in cold water because it can cause shivering and increase your body temperature.

How Long Does a Fever Typically Last?

How long a fever lasts depends on its type. For adults, most low-grade fevers resolve on their own after one or two days. You should be concerned about a fever that lasts at least three days.

High-grade fevers can sometimes last up to 14 days. When this happens, it indicates a serious condition that requires medical attention.

For children, fevers and accompanying flu-like symptoms can last anywhere from three to five days. Contact your doctor if symptoms (and the fever) last longer.

The body temperature that constitutes a fever varies slightly by age. In adults, a fever is a core temperature of 100.4 degrees F (38 degrees C) or higher. In children, a fever is a core temperature above 100.4 degrees F (38 degrees C) when their temperature is taken rectally.

While a fever is not always indicative of a serious health issue, there are times when medical attention is necessary, such as:

You should also seek immediate medical attention if your child has a febrile seizure. A febrile seizure lasts less than five minutes, during which your child may become stiff and exhibit twitching limbs. They may also lose consciousness or soil themselves.

Infants

In infants, a fever can be a sign of a serious medical condition and should not be ignored. For babies between 0-3 months, you should call your pediatrician if their body temperature gets above 100.4 degrees F (38 degrees C) or if the fever doesn’t go away after 24 hours.

For babies and toddlers between the ages of three months and three years, you should consult a doctor if their temperature reaches 102.2 degrees F (39 degrees C). Febrile seizures usually affect children in this age bracket. Contact your pediatrician if your child experiences a febrile seizure.

Children

For children above the age of 4, paying more attention to the symptoms accompanying the fever may be more important than their body temperature. Symptoms help signal whether a serious health issue is involved. Symptoms of a high-grade fever that requires medical attention include:

Nonetheless, medical experts recommend seeking emergency help if your child’s body temperature rises higher than 103 degrees F (39.5 degrees C). You should also visit a doctor if your child’s fever does not respond to home treatment or doesn’t go away after three days.

Adults

Fever does not automatically raise a call for concern for most adults. However, as with children, adults should seek medical help if their body temperature is elevated above 103 degrees F (39.5 degrees C). You should also consult a doctor if your fever does not respond to home and antipyretic medication.

For anyone in any age group who has a serious pre-existing condition such as heart disease, diabetes, cancer, HIV or anemia, getting a fever is a call to action. Contact your doctor or urgent-care facility and seek immediate medical attention.

One of the most effective ways to prevent a fever is maintaining good overall health and preventing the illnesses that can cause it. Limiting your exposure to infectious agents such as bacteria and viruses is a smart way to prevent numerous illnesses.  With exposure at school, camp and childcare, managing children’s health can feel challenging, but family conversations about preventive measures can help set life-long positive health habits.

Getting vaccinated can also help prevent a range of infectious diseases. Here are tips to reduce exposure to infectious agents:

A fever is one of the most common medical conditions. It is your body’s natural response when something is not right in your system, serving a crucial purpose by activating your immune response.

Depending on your age, underlying cause of the fever and existing medical conditions, a fever alone may or may not necessitate medical treatment. Although unpleasant, most fevers will resolve without specific medical attention.