What are the 5 stages of a fever?

September 24, 2025 •

4 min read

Over 90% of fevers are the body's natural response to fighting off an infection, serving a critical purpose in your immune defense. Understanding what are the 5 stages of a fever can provide clarity and help you manage symptoms effectively.

Quick Summary

The five stages of a fever, viewed from a clinical perspective, include the prodromal stage with vague symptoms, the chill stage as temperature rises, the flush stage when a new set point is reached, the defervescence stage as the fever breaks, and the post-fever recovery period, offering a clear progression of the body's response.

Key Points

Prodromal Stage: The initial phase of a fever, characterized by vague, non-specific symptoms like fatigue and mild aches before the temperature rises significantly.
Chill Stage: This phase involves feeling cold and shivering as the body actively raises its core temperature to a new, higher set point set by the hypothalamus.
Flush Stage: During this plateau phase, the body's temperature remains elevated and stable, and the patient may experience flushed, warm skin.
Defervescence Stage: This is when the fever breaks, and the body cools itself down through sweating and vasodilation as the temperature set point returns to normal.
Post-Fever Recovery: The final stage is the period following the fever's break, where the body recovers and residual symptoms of the underlying illness subside.
Medical Alert: While most fevers resolve naturally, a fever in an infant under three months or a high, persistent fever in an adult warrants medical consultation.

Introduction to Fever Progression

While often a source of discomfort, a fever is a protective mechanism orchestrated by your body's immune system. When the body detects a foreign invader, like a virus or bacteria, it releases substances called pyrogens. These pyrogens signal the hypothalamus, the brain's thermostat, to raise the body's temperature set point. This higher temperature creates a less hospitable environment for pathogens and boosts immune cell activity. The progression isn't always linear or obvious, but it can be broken down into distinct physiological phases, extending beyond a simple temperature reading.

Stage 1: The Prodromal Stage

This is the pre-fever phase where vague, non-specific symptoms begin to appear, signaling that your body is starting to respond to an underlying issue. This stage is often subtle and might not be directly associated with an impending fever. For many, it feels like they are 'coming down with something.'

Characteristics of the Prodromal Stage

Fatigue: A general feeling of tiredness and low energy is one of the most common early indicators.
Headache: A mild headache can develop as the body's immune system begins to ramp up.
Body Aches: A fleeting sense of aches and pains in the muscles and joints may occur.
Malaise: A general feeling of being unwell or discomfort.

During this time, the internal temperature is typically still within a normal range, but the body is beginning its metabolic preparations for the coming febrile response.

Stage 2: The Chill Stage (or Onset)

As the hypothalamus raises the body's temperature set point, the body initiates actions to increase heat production and conserve existing heat. This is the stage where the person actually feels cold, despite their core temperature rising.

The Body's Response During the Chill Stage

Shivering: The body induces muscle contractions (shivering) to generate heat.
Vasoconstriction: Blood vessels near the skin's surface constrict to limit heat loss, which can cause the skin to feel cold and appear pale.
Piloerection: The sensation of 'goosebumps' occurs as tiny muscles at the base of hair follicles contract.
Feeling of Cold: The person feels cold because their internal temperature is still below the new, higher set point dictated by the hypothalamus. This stage ends when the body's temperature reaches the new set point, and the person begins to feel warm again.

Stage 3: The Flush Stage (or Plateau)

Also known as the steady or plateau phase, this is the period where the fever is fully established and the body temperature has reached its new, higher set point. The shivering stops, and the body works to maintain this elevated temperature.

What to Expect During the Flush Stage

Elevated Temperature: The temperature remains consistently high, with only minor fluctuations over a 24-hour period.
Warm, Flushed Skin: The vasoconstriction of the chill stage reverses, and vasodilation occurs, causing the skin to feel warm and appear flushed as blood flow returns to the surface.
Other Symptoms: This stage is often accompanied by other fever symptoms like increased heart rate, headache, and decreased appetite.

Stage 4: The Defervescence Stage

This stage, also known as the fever 'break,' marks the turning point where the fever begins to subside. It happens when the underlying cause of the illness is overcome, or antipyretic medication is administered, causing the hypothalamus to lower the temperature set point back to normal.

Characteristics of Defervescence

Sweating: To cool the body down, the body initiates sweating (diaphoresis) to increase heat loss through evaporation.
Vasodilation: Blood vessels dilate further to bring heat to the surface of the skin, aiding in the cooling process. This can cause the person to appear red and feel warm to the touch.
Comfort: As the body temperature falls, the person typically starts to feel more comfortable and less ill.

Stage 5: The Post-Fever Recovery Period

Once the fever has broken and the body temperature has returned to normal, the body enters a recovery period. While the fever itself has ended, lingering symptoms from the illness may persist.

Actions During the Recovery Period

Hydration: It's crucial to rehydrate, as significant fluid loss can occur through sweating during defervescence.
Rest: Adequate rest is essential to allow the immune system to fully recover and regain strength.
Symptom Management: Other symptoms, like coughing or congestion, may still require management until the body fully heals.

Comparison of Fever Stages


Stage	Hypothalamus Set Point	Body Temperature	Key Physiological Response	Sensations for the Patient
Prodromal	Unchanged	Normal or slightly rising	Immune system activation	Mild aches, fatigue, malaise
Chill	Elevated	Rising rapidly	Shivering, vasoconstriction	Feeling of cold, chills
Flush (Plateau)	Elevated	Stable at a high level	Sustained high temperature	Feeling hot, flushed skin
Defervescence	Returning to normal	Falling	Sweating, vasodilation	Feeling warm and sweaty, relief
Post-Fever Recovery	Normal	Normal	Return to baseline function	Recovery from illness

When to Seek Medical Attention

While most fevers are self-limiting and resolve on their own, certain situations warrant a medical evaluation. For infants under three months, any fever should be immediately reported to a healthcare provider. For adults, a fever lasting more than three days or exceeding 103°F (39.4°C) requires medical attention. Accompanying severe symptoms, such as a stiff neck, confusion, breathing difficulties, or a purple spotted rash, are considered medical emergencies and require immediate care. The Centers for Disease Control and Prevention (CDC) provides extensive guidance on fever and illness, which can be found on their website [https://www.cdc.gov/].

Conclusion: Navigating the Phases of Fever

Understanding what are the 5 stages of a fever can demystify the process and help you recognize what your body is doing to fight an infection. From the initial, subtle warning signs of the prodromal stage to the final relief of defervescence and recovery, each phase serves a specific purpose in the immune response. By knowing what to expect, you can manage your symptoms more effectively and recognize when it's time to seek professional medical advice. Remember that while a fever can be uncomfortable, it is often a sign that your body's defenses are hard at work.

Frequently Asked Questions

A fever is most commonly caused by an infection from a virus or bacteria. The body's immune system releases pyrogens in response, which signal the hypothalamus in the brain to raise the body's temperature set point, helping to fight the infection.

No, treating a fever with medication isn't always necessary. Antipyretics are primarily used to alleviate discomfort. If the fever is mild and not causing significant distress, monitoring it is often sufficient, as the elevated temperature is part of the body's natural defense mechanism.

You shiver during the chill stage because your body's thermostat (the hypothalamus) has set a new, higher temperature. Since your current body temperature is still below this new set point, your muscles contract involuntarily (shiver) to generate more heat and reach the target temperature.

The key difference is regulation. In a fever, the hypothalamus raises the temperature set point in a controlled response. In hyperthermia, the body's temperature rises uncontrollably due to external factors like heatstroke, and the hypothalamic set point is unchanged.

No, this is a common misconception. The opposite is true. Your body requires energy and fluids to mount an immune response and fight the illness. It is important to stay hydrated and consume nutritious foods, even if your appetite is reduced.

An adult fever is concerning if it is 103°F (39.4°C) or higher, lasts more than three days, or is accompanied by severe symptoms like confusion, a stiff neck, or difficulty breathing.

A fever in an infant younger than three months can be a sign of a serious infection and may not present with the typical progression seen in older children or adults. Immediate medical attention is necessary to determine and treat the cause.