Hot and cold flashes are rapid, uncomfortable shifts in body sensation often experienced during an illness. These alternating feelings of heat and cold are a normal physiological response to fighting off an infection. They are not a sign of temperature control failure, but rather a temporary byproduct of the body working to reach or return from an elevated temperature. This process is triggered by the immune system initiating a fever.
The Body’s Temperature Regulation During Illness
The core cause of these temperature swings is the fever itself. When a pathogen enters the body, the immune system releases chemical messengers called pyrogens. These pyrogens travel to the hypothalamus, the brain’s temperature control center. Pyrogens trigger the production of prostaglandin E2 (PGE2), which temporarily raises the body’s desired temperature, or “set point,” above the normal 98.6°F (37°C). This elevated temperature is a defense mechanism intended to slow the reproduction of invading microorganisms.
The Sensation of Cold Flashes and Shivering
The feeling of a cold flash, or chills, signals the body’s initial attempt to reach the new, higher temperature set point. Since the actual body temperature is still below this elevated target, the person feels intensely cold. This prompts the body to actively generate and conserve heat. To raise the core temperature, the body uses peripheral vasoconstriction, narrowing blood vessels near the skin’s surface. This action reduces blood flow to the extremities, conserving internal heat, and simultaneously causes involuntary muscle contractions known as shivering. Shivering is a metabolically intense way to produce the heat necessary to match the new set point.
The Sensation of Hot Flashes and Sweating
The switch to a hot flash occurs when the hypothalamus lowers the temperature set point back toward a normal range. Once the set point drops, the body has a sudden excess of heat that it must rapidly shed, causing the feeling of being flushed or intensely hot. To cool down, the body initiates vasodilation, where blood vessels near the skin widen. This rushes warm blood to the surface, allowing heat to radiate away from the body. Sweat glands also become active, using evaporative cooling to shed excess heat and bring the temperature down.
Symptom Management and Warning Signs
Managing the discomfort of these temperature shifts involves simple steps focused on comfort and hydration. Layered clothing allows a person to easily adjust as they cycle between shivering and sweating, helping prevent becoming chilled after a hot flash. Maintaining fluid intake is important because sweating and fever can lead to dehydration. Over-the-counter fever-reducing medications, known as antipyretics, work by inhibiting the production of PGE2, lowering the hypothalamic set point and reducing the fever intensity.
When to Seek Medical Attention
Certain symptoms accompanying flashes and fever require immediate medical attention. Adults should seek care if a fever is 103°F (39.4°C) or higher, or if the fever is accompanied by:
- Mental confusion
- An unusual rash
- A stiff neck
- Persistent vomiting
- Difficulty breathing
- Extreme lethargy