Understanding What Can Spike a Fever: Causes and Management

October 1, 2025 •

4 min read

Approximately one-third of ambulatory care patients report fever to their primary care provider. Knowing what can spike a fever is key to understanding this common symptom, as it serves as a sign that the body's immune system is responding to an underlying issue.

Quick Summary

A fever is a temporary elevation in body temperature often initiated by infections like viruses and bacteria. Other potential triggers include autoimmune disorders, certain medications, and environmental factors such as heatstroke. The body's hypothalamus regulates temperature, but illness or other factors can alter this internal thermostat, resulting in a temperature increase. While many fevers improve with rest and fluids, a persistent or very high temperature may indicate a more serious condition requiring medical evaluation.

Key Points

Infections are the most common cause: Viruses like the flu and bacteria like those causing UTIs frequently spike a fever as the body's immune response is activated.
Hypothalamus controls temperature: The hypothalamus in the brain acts as the body's thermostat, raising the core temperature set-point during illness.
Non-infectious triggers exist: Fever can also be caused by autoimmune disorders, medication side effects, cancer, and heat-related illnesses.
Monitor high-risk individuals carefully: Infants under 3 months, older adults, and those with chronic conditions require special attention for any fever.
Home care focuses on comfort: Manage discomfort with rest, fluids, and over-the-counter medication, rather than just focusing on lowering the temperature.
Seek help for severe symptoms: Warning signs include confusion, severe headache, stiff neck, seizures, or difficulty breathing, which warrant immediate medical care.

What is a fever?

Fever, or pyrexia, is not an illness itself but a sign that the body is fighting something off. A fever occurs when the hypothalamus, the body's 'thermostat' located in the brain, raises the body's temperature set-point. This happens in response to pyrogens, which are fever-inducing substances released by the immune system or by invading pathogens like bacteria and viruses. For adults, a temperature of 100.4°F (38°C) or higher is typically considered a fever. The elevated temperature creates a less hospitable environment for viruses and bacteria, helping the immune system to work more effectively.

Common infectious causes

Most fevers are the result of an infection, either viral or bacterial. These infections trigger the immune system to release pyrogens, leading to a rise in body temperature.

Viral infections: Colds, flu, COVID-19, and RSV are common culprits. These illnesses often present with a fever alongside other symptoms such as cough, sore throat, and body aches. A fever with a viral infection may last for a few days before the body overcomes the virus.
Bacterial infections: Conditions like strep throat, urinary tract infections (UTIs), pneumonia, and bacterial gastroenteritis can cause a fever. Unlike viral infections, bacterial infections often respond to antibiotics prescribed by a healthcare provider.
Other infections: More serious infections such as meningitis, appendicitis, or certain skin infections (cellulitis) can also cause a fever, sometimes a very high one.

Non-infectious triggers

Sometimes, a fever can spike due to factors that are not infectious in nature. Recognizing these non-infectious causes is important for proper diagnosis and treatment.

Autoimmune and inflammatory diseases: Chronic inflammatory conditions, where the immune system mistakenly attacks the body's own healthy cells, can cause recurring fevers. Examples include rheumatoid arthritis, lupus, and inflammatory bowel disease (Crohn's disease and ulcerative colitis).
Medication side effects: Certain medications can interfere with the body's temperature regulation, leading to a drug-induced fever. Common offenders include some antibiotics, antihistamines, and seizure medications. This reaction typically resolves once the causative drug is stopped.
Heat-related illnesses: Extreme heat exposure, such as in cases of heatstroke or heat exhaustion, can cause a dangerous spike in body temperature. This is different from a fever in that the body's thermoregulatory center is overwhelmed, rather than reset.
Malignancies: In some cases, a fever can be a presenting symptom of cancer, particularly lymphomas or leukemia. These fevers are often referred to as 'fevers of unknown origin' when the cause is not immediately apparent.
Vaccinations: It is common for some people, especially children, to experience a low-grade fever for a day or two after receiving a vaccination as their body builds immunity.

Comparing infectious and non-infectious fevers


Feature	Infectious Fever	Non-Infectious Fever
Cause	Viruses, bacteria, or other pathogens.	Autoimmune diseases, medication side effects, heatstroke, or cancer.
Symptoms	Often accompanied by signs like sore throat, cough, body aches, or diarrhea.	May lack other typical infection-related symptoms; could involve a rash, joint pain, or confusion.
Duration	Usually short-lived (2-4 days) with viral infections; may be longer with bacterial issues.	Can be recurrent, chronic, or of unknown origin (FUO).
Response to Management	May respond to fever-reducing medication for comfort, but underlying infection needs specific treatment.	Resolves by addressing the underlying cause (e.g., stopping medication, managing the autoimmune condition).

What to do for a spiking fever

When a fever spikes, the primary goal is to manage discomfort and support the body's natural healing process. This includes:

Hydrate: Drink plenty of fluids, such as water, clear soups, or oral rehydration solutions, to prevent dehydration.
Rest: Get plenty of rest to allow the body to recover.
Medication: Over-the-counter fever reducers can help reduce the fever and alleviate discomfort. Always follow product instructions and consult a healthcare professional regarding appropriate use.
Cooling measures: Use a cool, damp washcloth on the forehead or neck. Wearing lightweight clothing and using a light blanket can also help.

When to seek medical attention

While most fevers are not serious, it's crucial to know when to consult a healthcare provider. The following are reasons to seek medical care:

An infant under 3 months with a rectal temperature of 100.4°F (38°C) or higher.
A fever of 105°F (40.5°C) or higher in any age group.
A fever that persists for more than 48-72 hours, or one that comes and goes for more than a week.
Fever accompanied by a stiff neck, severe headache, confusion, seizures, or a new rash.
Difficulty breathing, chest pain, or severe abdominal pain with a fever.
If the person is in a high-risk group, such as having a weakened immune system, a chronic health condition, or recent travel history.

Conclusion

A spiking fever can be caused by a wide range of issues, from common viral and bacterial infections to more complex autoimmune conditions or even environmental heat exposure. The fever itself is a sign that the body's immune system is active, but monitoring the temperature and accompanying symptoms is crucial. By staying hydrated, resting, and knowing when to seek professional help, you can effectively manage a fever and address its underlying cause. While most fevers are harmless and resolve on their own, recognizing the warning signs of a serious condition is vital for proper care.

For more detailed information on fever management and symptoms, consult trusted medical resources like the Mayo Clinic website.

Frequently Asked Questions

For adults, a fever is generally considered dangerous and requires immediate medical attention if it reaches 105°F (40.5°C) or higher. In infants under 3 months, a rectal temperature of 100.4°F (38°C) or higher is always considered a medical concern.

Yes, some medications can cause a drug-induced fever as a side effect. This can happen with certain antibiotics, antihistamines, and anti-seizure drugs, and typically resolves after the medication is discontinued.

No, a high fever does not always mean the illness is serious. Severity is better assessed by how the person looks and acts, rather than the exact temperature. A mild viral infection can sometimes cause a high fever, while a serious infection might cause a low-grade or no fever at all.

Body temperature naturally fluctuates throughout the day and is often at its highest in the late afternoon and evening. When the body is fighting an infection, this natural cycle can make fever symptoms feel worse at night.

While emotional stress can affect body temperature regulation, it is not a direct cause of a true fever (pyrexia). Chronic inflammation triggered by stress may contribute, but infections, autoimmune disorders, and other conditions are the primary drivers of fever.

In a fever, the body's internal thermostat (the hypothalamus) is reset to a higher temperature in response to pyrogens. Hyperthermia, on the other hand, is an uncontrolled rise in body temperature due to external factors like extreme heat, with the hypothalamus's set-point remaining normal.

Not necessarily. A fever is a natural defense mechanism. Medication should be used to alleviate discomfort rather than just to lower the temperature. For a mild fever with no other symptoms, rest and fluids may be all that is needed.