Fever - Symptoms and Causes

About Fever

Fever is a rise in body temperature that happens when the immune system fights an infection. Most fevers in adults and children cause discomfort but aren’t dangerous. However, infants with even slight fevers may have serious infections.

Fevers typically last only a few days. There are several over-the-counter medications that can lower fever. These include acetaminophen (Tylenol) and ibuprofen (Advil, Motrin).

Not every fever requires treatment. If the fever isn’t causing significant discomfort, it’s often better to let it run its course. The fever itself helps the body fight infection.

For comfort during a fever:

Drink plenty of fluids
Rest
Dress in light clothing
Use a light blanket if feeling chilled

When to seek medical help:

Infants under 3 months with any fever
Very high fever (above 103°F or 39.4°C)
Fever lasting more than three days

Signs of Fever

Fever is when body temperature rises above normal. Most people have a normal temperature around 98.6°F (37°C). When a mouth thermometer reads 100°F (37.8°C) or higher, this is usually considered a fever.

Someone with a fever might experience:

Sweating
Chills and shivering
Headache
Muscle aches
Poor appetite
Irritability
Dehydration
Weakness

Measuring Temperature

You can check for fever using different types of thermometers. Options include:

Thermometer Type	Features
Oral (mouth)	Very accurate, easy to use
Rectal	Most accurate, best for infants
Ear (tympanic)	Convenient but less accurate
Forehead (temporal)	Easy to use, but less precise

Oral and rectal thermometers give the most reliable readings of core body temperature. While ear and forehead thermometers are easier to use, they don’t measure temperature as accurately.

Rectal temperatures offer more accurate readings for babies when possible. When talking to your doctor, always mention both the temperature reading and the type of thermometer you used.

When to Get Medical Help for a Fever

Babies and Very Young Children

Fevers in babies need closer attention than in older children or adults. Contact your child’s doctor if:

Your baby is under 3 months old with a temperature of 100.4°F (38°C) or higher
Your baby is 3–6 months old with a temperature above 102°F (38.9°C)
Your baby is 3–6 months old, has a fever, and seems unusually fussy, tired, or uncomfortable
Your child is 7–24 months old with a fever over 102°F (38.9°C) lasting more than a day
Your young child has a fever with other concerning symptoms

School-Age Children

Most fevers in children aren’t dangerous if they are still responsive, making eye contact, drinking fluids, and are somewhat playful.

Call the doctor if your child:

Seems confused, listless, or won’t make eye contact
Is very irritable or has troubling symptoms, such as:
- Repeated vomiting
- Bad headache
- Severe sore throat
- Painful stomach
Has a fever after being in a hot car (seek help immediately)
Has a fever lasting more than three days
Has a seizure with the fever (call 911 if it lasts over five minutes)

Children with immune system issues or other health conditions should get specific advice from their doctor on when to seek help for fevers.

Grown-Ups

For adults, contact your doctor if your temperature reaches 103°F (39.4°C) or higher.

Get immediate medical care if you have a fever plus any of these:

Severe headache
Unusual rash
Light sensitivity
Stiff neck
Confusion or unusual behavior
Persistent vomiting
Breathing problems or chest pain
Stomach pain
Painful urination
Seizures

Causes

The hypothalamus, often considered the body’s internal thermostat, controls the body’s temperature balance. This brain region expertly regulates the balance between heat production and heat loss.

Body temperature naturally varies throughout the day, usually being lower in the morning and higher by late afternoon, even in healthy people.

When illness strikes, the immune system can trigger the hypothalamus to raise body temperature intentionally. This creates a fever, which involves complex bodily processes that generate more heat while reducing heat loss.

Shivering is one way your body produces additional heat, while seeking a blanket helps retain warmth.

Fevers below 104°F (40°C), often from viruses like the flu, can boost immune function and are usually not harmful.

Several factors can lead to elevated body temperature:

Infections: Both viral and bacterial infections commonly cause fevers.
Heat-related conditions: Heat exhaustion can elevate body temperature.
Inflammatory disorders: Conditions like rheumatoid arthritis, which inflames joint linings.
Cancerous tumors: Malignancies may trigger fevers.
Medications: Some antibiotics, blood pressure medications, and seizure medications.
Vaccinations: Including DTaP, pneumococcal, and COVID-19 vaccines.

Complications

Febrile seizures mostly affect children between 6 months and 5 years old. If your child has one febrile seizure, there’s about a 33% chance they’ll have another, typically within the next year.

These seizures can be scary to witness. Signs include:

Loss of consciousness
Shaking of arms and legs on both sides
Eyes rolling backward
Body stiffness

What to do during a seizure:

Place your child on their side or stomach
Clear away any sharp objects
Loosen tight clothing
Gently hold them to prevent injury
Don’t put anything in their mouths
Don’t try to stop the seizure

When to seek medical help:

Call 911 if the seizure lasts more than 5 minutes
Get emergency care if it is your child’s first febrile seizure
Visit your child’s doctor soon after any febrile seizure

Ways to Prevent Fevers

Reducing your exposure to germs can help prevent fevers. Taking simple steps each day makes a big difference in keeping illness away.

Vaccinations are one of the best defenses. Receive vaccinations for illnesses such as the flu and COVID-19 to strengthen your immunity. Adhering to the latest health guidelines on mask-wearing and social distancing significantly lowers your risk.

Hand Hygiene Is Crucial:

Wash hands frequently, especially after being in public places.
Use soap and water, cleaning both front and back thoroughly.
Carry hand sanitizer for times when washing isn’t possible.

Instill in children the essential practice of effective handwashing. Show them how to wash completely under running water with soap.

Avoid touching your face, particularly your eyes, nose, and mouth. These are main entry points for germs that cause infections and fevers.

Additional Prevention Tips:

Cover coughs and sneezes with your elbow.
Turn away from others when you are coughing or sneezing.
Don’t share cups, water bottles, or eating utensils.
Stay home when feeling unwell.