While not every person experiences a fever when they have a virus, a fever can be a sign that the body is trying to fight off the infection.
Most viral illnesses will improve with time and supportive treatments such as cold compresses and over-the-counter (OTC) medications. However, having a body temperature that is too high may require medical attention.
The symptoms of a viral fever will vary depending on the virus.
A fever is the body’s natural reaction to exposure to disease-causing pathogens, such as viruses and bacteria.
The body’s increase in temperature can destroy the proteins in these pathogens to keep them from multiplying. Also, fever is an inflammatory response to the illness in the body.
The definition of a fever depends on a person’s age and where the temperature reading originates from.
According to the Seattle Children’s Hospital, the following are indicators of a fever in children:
- Rectal, ear, or forehead: The temperature is higher than 100.4°F (38.0°C).
- Oral: The temperature is higher than 100°F (37.8°C).
- Under the armpit: The temperature is higher than 99°F (37.2°C).
The definition of fever can vary in adults. However, many doctors will consider a body temperature reading using an oral thermometer that is higher than 100°F (37.8°C) as a fever.
A viral fever can cause a person to feel fatigued, irritable, and achy. Additional symptoms may vary based on the virus causing the underlying illness.
For example, the roseola virus causes a fever for 2–3 days in children, followed by a rash that starts about 12–24 hours after the fever subsides.
There are many potential causes of viral illness, which may include cold and flu viruses.
Sometimes, a bacterial illness follows a viral one. This can make it difficult to tell the difference between the two and determine when a person may benefit from taking antibiotics.
Fevers without any other apparent underlying illness can be especially common in young children.
In a study of 75 children with a fever but no other signs of bacterial infection, the results of which appeared in the journal Pediatrics, an estimated 76 percent had one or more viruses in their system.
The most common viruses present were the adenovirus, human herpesvirus 6, enterovirus, and parechovirus. The paper estimated that less than 1 percent of fever-related illnesses with no appearance of a clear source in children under 3 were due to bacterial infections.
This means that viruses are an especially common cause of fevers among young children. Keeping this information in mind is important, as taking antibiotics will be ineffective in treating viral infections.
An infected person can spread a viral illness by sneezing, breathing, or touching people or surfaces. Practices such as washing the hands frequently and often disinfecting surfaces can help keep these illnesses at bay.
A doctor will take a person’s health history and ask questions about their symptoms when diagnosing a potential viral fever. Examples of these questions may include when a person first noticed the symptoms and what makes these symptoms worse or better.
A doctor may order tests to identify the presence of viruses in a person’s blood, sputum, or urine.
For example, a rapid influenza diagnostic test involves taking cell samples from the back of the throat and testing them for the presence of influenza A or B proteins.
Not all tests for viral illnesses are available so quickly, however. In fact, some may require laboratory analysis to identify the specific virus.
However, it is not always necessary to send tests to the laboratory to diagnose a viral fever. A doctor may take into account a person’s symptoms to make this diagnosis.
According to Seattle Children’s Hospital, viruses cause an estimated 10 times the amount of infections that bacteria do.
A lukewarm bath can help relieve the symptoms of a fever.
Treatment for a viral fever depends upon the underlying cause, the degree of the fever, and other symptoms a person may be experiencing.
For example, a fever greater than 104°F (40°C) for children and 103°F (39.4°C) for adults can be a medical emergency. A person likely has a serious viral infection if their body temperature equals or exceeds these numbers.
For lower-grade fevers, treatments may include the following:
- Taking OTC medications: Ibuprofen and acetaminophen are both OTC medications that can relieve fever. Aspirin can also do this, but people under 18 should not take aspirin due to the risks of a condition called Reye’s syndrome. Antibiotics will not treat a fever due to viral illness.
- Taking lukewarm baths: These can also soothe a feverish body.
- Drinking cooled fluids: Sipping on cool water or electrolyte-containing solutions can help cool body temperatures and prevent dehydration related to illness.
A common misconception regarding fever is that using very cold water in a bath or applying it to the skin is effective. In actual fact, exposure to excessively cold temperatures can have an adverse effect on the body. A person should use lukewarm water for a bath instead.
If a person has a fever for longer than 3 days, or they have a temperature higher than 103°F (39.4°C) in adults, 102°F (38.9°C) in children, or 100.4°F (38°C) in infants, they should seek medical attention.
Body temperatures higher than this can cause seizures, hallucinations, and confusion, and they are symptoms of a more serious illness.
Viruses can cause fevers that may or may not result in other symptoms.
Most viruses will go away with time and supportive measures. However, if a viral fever is too high, a person should seek medical attention.