Fever Causes: Why Your Temperature Rises and What to Do

A fever is a temporary increase in body temperature, often acting as a sign that the body's immune system is responding to an infection or inflammation. While the average temperature is 98.6°F, a fever is typically defined as 100.4°F or hig

Medically reviewed by Dr. Roshan Basnet, MBBS, MD (Internal Medicine) on 2026-08-25. See the medical review policy.

Introduction

When to get emergency help

Call an ambulance or go to your nearest emergency department now if you have a sudden severe headache, chest pain, trouble breathing, coughing up blood, black or bloody stools, a stiff neck with fever, a rash that does not fade when pressed, slurred speech, one-sided weakness, confusion, a seizure, fainting, or thoughts of harming yourself.

A fever, medically known as pyrexia, is a temporary increase in body temperature. While the average is 98.6°F (37°C), it's normal to have slight fluctuations. A fever is generally a temperature of 100.4°F (38°C) or higher. Importantly, a fever is not a disease but a signal from your immune system that something is wrong.

When the body detects a threat, the hypothalamus—the brain's thermostat—may reset to a higher temperature. This heat helps the immune system work better and makes it harder for pathogens to survive. While uncomfortable, fever often plays a key role in defense. However, persistent or very high temperatures may need medical evaluation.

Common Causes

The most frequent triggers are related to the body's response to external pathogens:

• Viral Infections: The common cold, flu, and COVID-19 are among the most frequent causes.
• Bacterial Infections: Strep throat, urinary tract infections (UTIs), and pneumonia can cause fever.
• Gastroenteritis: Stomach flu from viruses, bacteria, or parasites may lead to fever with digestive upset.
• Ear Infections: Especially in children, middle ear infections can spike temperature.
• Skin Infections: Cellulitis and other skin infections may cause redness, warmth, and fever.
• Immunizations: Low-grade fever after vaccines is common and shows the immune system is responding.
• Heat Exhaustion: Overheating from high temperatures or intense activity can raise core temperature.

Less Common Causes

While infections are primary, other issues can cause fever:

• Autoimmune Disorders: Conditions like rheumatoid arthritis or lupus may cause chronic fever.
• Malignancies: Some cancers, especially leukemia and lymphoma, may lead to persistent fever, often at night.
• Blood Clots: Deep vein thrombosis or pulmonary embolism can trigger inflammation and low-grade fever.
• Certain Medications: Drug fever can occur from antibiotics, anti-seizure drugs, or blood pressure medications.

Associated Symptoms

Fever rarely appears alone. Common accompanying signs include:

• Chills and Shivering: As the body raises its temperature, you may feel cold.
• Sweating: When the fever breaks, the body cools through perspiration.
• Headache and Muscle Aches: Systemic inflammation causes body aches.
• Dehydration: Higher temperature increases fluid loss; thirst and dark urine are signs.
• Fatigue and Weakness: The immune response demands energy, causing lethargy.
• Loss of Appetite: Many people eat less when fighting infection.

Diagnosis

To find the cause, a healthcare provider takes a history and does a physical exam. They ask about duration, highest temperature, recent travel, or exposure. They may check for infection in ears, throat, lungs, and abdomen. Tests may include blood work (CBC), urinalysis, or imaging like X-rays if pneumonia is suspected. For persistent fever of unknown origin, more specialized tests for autoimmune conditions may be needed.

Treatment Options

Treatment goals focus on comfort, as fever itself helps fight infection. General approaches include:

• Hydration: Drink plenty of fluids like water, broth, or oral rehydration solutions.
• Rest: Allow the body to direct energy to the immune response.
• Cooling Measures: Wear lightweight clothing, keep room temperature comfortable, and use lukewarm sponge baths if needed.
• Monitoring: Track temperature to share with a healthcare provider if fever persists.

Medicines Sometimes Used

Medications may be recommended to reduce discomfort. Use only as directed by a doctor or label instructions:

• Acetaminophen: Reduces fever and relieves aches.
• Ibuprofen: An NSAID that lowers temperature and reduces inflammation.
• Aspirin: For adults only; never give to children or teenagers due to Reye’s syndrome risk.
• Antibiotics: Only effective for bacterial infections; not for viral fevers.

When to See a Doctor

While many fevers are harmless, certain red flags require immediate medical attention. Contact a healthcare provider if:

• Fever lasts longer than three days without improvement.
• Temperature exceeds 103°F (39.4°C) in adults.
• An infant under 3 months has a rectal temperature of 100.4°F (38.0°C) or higher.
• Severe headache, stiff neck, or sensitivity to light.
• Persistent rash or unusual bruising.
• Confusion, difficulty breathing, or chest pain.
• Persistent vomiting or signs of severe dehydration.

FAQ

1. Is a fever always a bad sign? Not necessarily; a fever is usually a sign that the immune system is working correctly to fight off an intruder.
2. Can teething cause a high fever in babies? Teething may cause a very slight rise in temperature, but it is rarely associated with a true fever over 100.4°F.
3. Should I "starve a fever"? No, the body needs calories and significant hydration to fuel the immune system during an illness.
4. Why do fevers get worse at night? The body's natural circadian rhythm can cause temperatures to peak in the evening, and immune activity often increases during sleep.
5. Can stress cause a fever? Some people may experience "psychogenic fever," where emotional stress leads to a slight increase in body temperature.

Summary

A fever is a common physiological response to infection, inflammation, or other underlying triggers. While it can cause discomfort, it is often a sign that the body is actively defending itself. By monitoring associated symptoms and seeking medical advice when warning signs appear, individuals can safely manage fevers and address their root causes.

Medical Disclaimer: This content is for educational purposes only and does not replace professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any medication.