Fever: Causes, Symptoms, and When to Seek Help

What is Fever?

A fever is a temporary increase in body temperature, often due to an illness. Having a fever is a sign that something out of the ordinary is going on in your body. For an adult, a fever may be uncomfortable, but usually isn't a cause for concern unless it reaches 103 F (39.4 C) or higher. For infants and toddlers, a slightly elevated temperature may indicate a serious infection.

Normal body temperature varies throughout the day — it's lower in the morning and higher in the late afternoon and evening. Although most people consider 98.6 F (37 C) normal, your body temperature can vary by a degree or more, from about 97 F (36.1 C) to 99 F (37.2 C), and still be considered normal (Mayo Clinic).

Common Causes

Fever occurs when an area in your brain called the hypothalamus (hi-poe-THAL-uh-muhs) — also known as your body's "thermostat" — shifts the set point of your normal body temperature upward. When this happens, you may feel chilled and add layers of clothing, or you may shiver to generate more body heat, eventually resulting in an elevated body temperature.

Common causes of fever include:

• Infections: Most fevers are caused by infections or other illnesses. Fever helps the body fight infections by stimulating natural defense mechanisms.
• Viral infections: Such as colds, flu, COVID-19, and other respiratory illnesses.
• Bacterial infections: Including urinary tract infections (UTIs), pneumonia, and ear infections.
• Heat exhaustion: Exposure to high temperatures can lead to fever, particularly if dehydration occurs.
• Inflammatory conditions: Such as rheumatoid arthritis or inflammatory bowel disease (IBD).
• Medications: Some drugs, including antibiotics and drugs used to treat high blood pressure or seizures, can cause fever.
• Immunizations: Vaccines such as the pneumococcal vaccine, diphtheria-tetanus-acellular pertussis (DTaP), and COVID-19 vaccines can cause fever as a side effect.
• Teething in infants: While not a major cause of high fever, teething can lead to a slight increase in body temperature.
• Autoimmune diseases: Conditions like lupus can cause prolonged or recurrent fevers.
• Cancer: Fever can be an early sign of certain cancers, such as leukemia and lymphoma.

Associated Symptoms

Depending on what's causing your fever, additional signs and symptoms may include:

• Sweating
• Chills and shivering
• Headache
• Muscle aches
• Loss of appetite
• Irritability
• Dehydration
• General weakness

Children between the ages of 6 months and 5 years might experience febrile seizures. About a third of the children who have one febrile seizure will have another one, most commonly within the next 12 months. Febrile seizures are generally harmless and do not indicate a long-term or ongoing problem (CDC).

When to See a Doctor

Fevers by themselves may not be a cause for alarm, but you should seek medical advice in the following situations:

• If an infant younger than 3 months has a rectal temperature of 100.4 F (38 C) or higher.
• If a child between 3 and 6 months has a rectal temperature up to 102 F (38.9 C) and seems unusually irritable, lethargic, or uncomfortable, or has a temperature higher than 102 F (38.9 C).
• If a child between 6 and 24 months has a rectal temperature higher than 102 F (38.9 C) that lasts longer than one day but shows no other symptoms. If there are other symptoms, such as a cold, cough, or diarrhea, you might call your child's doctor sooner based on severity.
• If an adult has a temperature of 103 F (39.4 C) or higher.
• If an adult has a fever for more than three days.
• If the fever is accompanied by severe symptoms such as severe headache, rash, sensitivity to bright light, stiff neck, mental confusion, persistent vomiting, difficulty breathing, abdominal pain, or pain when urinating.

Diagnosis

To diagnose the cause of a fever, your doctor will perform a physical exam and ask questions about your symptoms and medical history. Depending on the suspected cause, your doctor may order additional tests, such as:

• Blood tests: Such as a complete blood count (CBC) to check for signs of infection or other abnormalities.
• Urinalysis: To check for a urinary tract infection.
• Chest X-ray: To look for signs of pneumonia.
• Throat swab: To test for strep throat or other bacterial infections.
• Lumbar puncture (spinal tap): If your doctor suspects meningitis, a sample of cerebrospinal fluid may be collected for testing.
• Imaging tests: Such as CT scans or MRIs to look for abscesses or other sources of infection.

In some cases, especially if the fever is persistent and the cause is unclear, your doctor may recommend a watchful waiting approach or further specialized testing.

Treatment Options

Treatment for fever depends on the cause. In general, if the fever is mild and you're otherwise healthy, you may not need treatment. However, if the fever is causing discomfort, your doctor may recommend over-the-counter medications such as:

• Acetaminophen (Tylenol, others): This is generally safe for most people, but follow the recommended dosage to avoid liver damage.
• Ibuprofen (Advil, Motrin IB, others): Use caution when giving aspirin to children or teenagers, as it has been linked to Reye's syndrome, a rare but potentially life-threatening condition.

For more serious infections causing fever, your doctor may prescribe antibiotics or antiviral medications. It's important to complete the full course of any prescribed medication.

Home Remedies

You can also take steps to manage fever at home:

• Stay hydrated: Drink plenty of fluids to prevent dehydration.
• Rest: Get plenty of sleep to help your body recover.
• Stay cool: Dress lightly and keep the room temperature comfortable. You might use a lukewarm sponge bath to help bring down a fever, but avoid cold baths or ice as these can cause shivering and raise body temperature.
• Eat lightly: Stick to easy-to-digest foods if you have a decreased appetite.

Prevention Tips

While not all fevers can be prevented, you can reduce your risk by practicing good hygiene and taking steps to avoid infections:

• Wash your hands frequently: Use soap and water, especially before eating, after using the toilet, and after being in public places.
• Cover your mouth and nose: When coughing or sneezing, use a tissue or your elbow to prevent the spread of germs.
• Stay up to date on vaccinations: This includes annual flu shots and other recommended vaccines.
• Avoid close contact with sick individuals: This can help reduce your exposure to infectious diseases.
• Practice safe food handling: Cook foods to proper temperatures and avoid cross-contamination to prevent foodborne illnesses.
• Stay hydrated and eat a balanced diet: A healthy lifestyle supports a strong immune system.

Emergency Warning Signs

Seek emergency medical care if you or someone else has a fever and any of the following signs or symptoms:

• Difficulty breathing or chest pain
• Severe headache or stiffness in the neck
• Confusion or irritability
• Persistent vomiting or inability to keep fluids down
• Seizures or convulsions
• Rash or bruising
• Difficulty waking up or lack of responsiveness
• Blue lips, tongue, or nails
• Extreme lethargy or inability to move

These symptoms can indicate a serious or life-threatening condition that requires immediate medical attention. Do not wait to see if the fever improves on its own in these cases.

For more information on fever and its management, you can refer to reputable sources such as the Mayo Clinic, Centers for Disease Control and Prevention (CDC), and the World Health Organization (WHO).