Fever Causes, Treatment and When To See a Doctor

A fever can be uncomfortable, confusing and, at times, concerning — especially for parents. While most fevers are caused by common illnesses and improve on their own, some situations need medical care right away.

Discover what causes fevers, how to treat them and when it’s time to see a doctor.

What is a fever?

Many people say they have a “low-grade fever,” but medically speaking, a fever has a clear definition.

Jake Moore, DO, medical director of ProMedica Urgent Care, shares that a fever is a temperature of 100.4 degrees Fahrenheit or greater. Anything less than that is not a fever.

Temperatures below that level can change during the day due to activity, the environment or natural body heat control. Once a temperature reaches 100.4 degrees or higher, the body is responding to something more significant.

Why the Body Creates a Fever

A fever is part of the body’s natural defense system. When viruses or bacteria enter the body, the immune system raises the body’s temperature. This makes it harder for germs to survive and spread.

“Your body creates a fever to make it so your body is less hospitable to harmful viruses or bacteria,” Dr. Moore says.

In many cases, a fever is a sign that the immune system is doing exactly what it’s meant to do.

Common Causes of Fever

Dr. Moore shares that the most common cause of a fever is a viral illness.

“Viral illnesses are sicknesses like COVID-19, influenza and respiratory syncytial virus (RSV). These can all lead to a temperature of 100.4 or greater,” he says.

Other common causes of fever include:

• Pneumonia
• Urinary tract infections
• Bacterial sinus infections
• Strep throat
• Skin infections, such as cellulitis

Children can develop fevers for additional reasons. Teething or emotional stress may raise a child’s temperature, particularly in younger age groups. Parents should still monitor symptoms closely and contact their child’s primary care provider if they have concerns.

How To Treat a Fever at Home

If symptoms are mild and the fever is manageable, treatment at home is often appropriate. The focus should be on comfort, hydration and rest. “Drink plenty of fluids and get plenty of rest,” Dr. Moore recommends.

Over-the-counter pain relievers can be taken to reduce fever and discomfort. “Tylenol is the best fever reducer, and it helps with overall body aches,” Dr. Moore says.

If symptoms worsen, last longer than expected or you’re unsure whether home care is enough, your primary care provider or urgent care provider can help determine next steps.

When Adults Should See a Doctor for a Fever

A fever may be a sign that medical evaluation is needed, especially if it reaches or exceeds the clinical threshold.

“If it’s 100.4 or greater, you should make an appointment with your doctor,” Dr. Moore says.

In many cases, adults can start by contacting their primary care provider. If an appointment isn’t available or symptoms need more immediate attention, urgent care providers can evaluate fevers, identify common infections and help guide treatment.

You should seek medical care right away if a fever is accompanied by:

• Persistent nausea or vomiting
• Lightheadedness, dizziness or fainting
• Confusion or disorientation
• Conditions or medications that weaken the immune system

Those with a history of IV drug use or those who are immunocompromised should seek emergency care if they develop a fever.

Fevers in Babies and Children

Age plays an important role in how fevers are handled. In newborns, any fever is considered a medical emergency.

“If your newborn has a fever of 100.4 degrees or greater, you need to go to the emergency room 100% of the time,” Dr. Moore says.

For older infants and children, behavior is often more important than the number on the thermometer. Fevers in children who are eating, drinking and urinating normally can often be managed at home with fluids and medication.

Tylenol is the best fever reducer and pain reliever for children. Avoid giving Aspirin to children under the age of 18 unless directed to do so by a health care provider. Contact your child’s pediatrician or primary care provider for additional guidance.

If your child has reduced wet diapers, is refusing to eat or drink, or experiences changes in alertness, seek immediate medical attention.

Febrile Seizures in Children

Another common occurrence that comes along with fevers in babies are febrile seizures. They can be alarming, but they’re not usually dangerous long term.

“It’s important to understand that if your child has one febrile seizure it doesn’t mean that they’re going to get another one if they have another fever, nor does it mean that they’re likely to have epilepsy or seizures in the future,” Dr. Moore says.

If a febrile seizure occurs, place the child on their side, remove any nearby objects and start a timer so that you know how long the seizure lasts. Seek emergency care once the seizure ends.

When It’s Safe To Return to Work or School

Returning to normal activities too soon can spread illness to others. Dr. Moore recommends being fever-free without the use of fever-reducing medication for at least 24 hours before going back to work, school or other group settings.

This guidance helps protect coworkers, classmates and family members from getting sick.

Fevers are common and often part of the body’s normal response to illness, but they should never be ignored. Understanding what causes a fever — and knowing when to reach out to a primary care provider, visit urgent care or seek emergency care — can keep you and your family safe.

Jake Moore, DO
Dr. Moore is the medical director of ProMedica Urgent Care. View his profile.