📖 Fever Basics: Understanding Normal Temperature, Types of Fever & When to Worry

A complete guide to the fundamentals of fever — by Dr. Ravi Sishir Reddy, MD

Fever is one of the most common reasons people seek medical care, yet it remains widely misunderstood. A fever is not a disease — it’s the body’s natural defence mechanism against infection. It raises the body’s temperature to make it harder for viruses and bacteria to survive, while simultaneously activating the immune system. In this pillar guide, Dr. Ravi Sishir Reddy explains the basics of fever: what is normal, what causes a temperature to rise, how to measure it correctly, and how to distinguish a simple fever from a serious one.

1. What Is Fever & Normal Body Temperature?

The average normal body temperature is 98.6°F (37°C), but it can vary by about 1°F throughout the day — lower in the morning, higher in the late afternoon. A true fever is generally defined as a temperature above 100.4°F (38°C) measured with a reliable thermometer. This article explains what happens inside your body when you have a fever and how the immune system uses heat to fight off pathogens.

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2. Fever in Adults: When to Worry

Most fevers in healthy adults are self‑limiting and resolve within a few days. But certain symptoms accompanying a fever — severe headache, stiff neck, chest pain, confusion, or difficulty breathing — indicate a serious underlying condition. Learn the red flags that mean it’s time to see a doctor or go to the emergency room.

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3. Fever in Children (Pediatric Advice)

Parents are often alarmed by a child’s fever, but fever itself is not dangerous — it’s the underlying cause that matters. Understand how to measure temperature in infants and children, when a fever is a sign of a serious infection, and how to manage it safely with medications and fluids.

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4. Fever in the Elderly: Special Considerations

Older adults may not mount a high fever even with a serious infection. A temperature that seems “normal” could actually be elevated for them. A low‑grade fever, confusion, or a drop in functional status in an elderly person should always be investigated. Dr. Reddy explains why fever evaluation differs in seniors.

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5. Viral Fever vs. Bacterial Infection

How do you tell if a fever is caused by a virus or bacteria? Viral fevers often come on gradually, are accompanied by body aches and cough, and improve on their own. Bacterial infections may cause higher fevers, localised symptoms (like a sore throat with pus or burning urination), and may require antibiotics. Learn the clues that help distinguish the two.

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6. Low‑Grade Fever: Causes & Concerns

A persistent low‑grade fever (99°F–100.4°F) that lasts for weeks can be puzzling. It may be due to a lingering viral infection, stress, hormonal changes, autoimmune disease, or even certain medications. Dr. Reddy outlines the most common causes and the investigations your doctor may recommend.

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7. High‑Grade Fever (103°F and Above)

A temperature above 103°F (39.4°C) can be alarming and often indicates a more serious infection. This article covers the possible causes — from severe influenza and pneumonia to meningitis and sepsis — and the steps to take when the mercury climbs high.

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8. Fever of Unknown Origin (FUO)

When a fever persists for more than three weeks without a clear cause despite extensive testing, it is labelled a “Fever of Unknown Origin.” FUO can be caused by hidden infections, autoimmune diseases, or malignancies. This article explains the diagnostic journey and what to expect.

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9. How to Check Temperature Correctly

Using the right thermometer and technique is essential for an accurate reading. Dr. Reddy explains the pros and cons of oral, axillary (armpit), tympanic (ear), temporal (forehead), and rectal thermometers. A step‑by‑step guide ensures you get a reliable measurement every time.

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10. Fever Myths: Cold Baths, Alcohol Rubs & More

Should you take a cold shower to bring down a fever? Is rubbing alcohol on the skin effective? Does teething cause high fever? Dr. Reddy debunks the most common myths and explains which popular remedies can actually be dangerous.

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Understanding the basics of fever empowers you to respond appropriately — neither panicking over a mild temperature nor ignoring a serious one. Dive into the articles above to learn everything you need to know about fever, and always consult your doctor if you are unsure about your symptoms.