The sensation of feeling intensely cold, often accompanied by uncontrollable shivering and chills, while the body simultaneously feels hot or has a high core temperature, is a common biological paradox. This feeling represents a temporary miscommunication within the body’s temperature regulation system. It is evidence that the body’s built-in defenses are actively working to raise the internal temperature to a new, higher goal. Understanding this process requires looking at the body’s internal thermostat and how it can be temporarily reset.
The Body’s Internal Thermostat
The core of temperature regulation is the hypothalamus, a small area in the brain that functions like the body’s thermostat, maintaining a narrow, normal core temperature range, typically around 98.6°F (37°C).
During illness, the immune response releases fever-inducing substances called pyrogens. These pyrogens act on the hypothalamus, raising its temperature set point. When the hypothalamus resets its target temperature to a higher level, the body perceives its current temperature as too cold relative to this new target, causing the sensation of coldness.
To close this gap, the hypothalamus initiates heat-generating actions. Two primary mechanisms are triggered: peripheral vasoconstriction and shivering. Vasoconstriction narrows blood vessels near the skin, reducing heat loss and making the skin feel hot. Shivering involves rapid, involuntary muscle contractions that generate heat through increased metabolic activity.
The intense cold and uncontrollable shaking (rigor) are the physical manifestation of the body attempting to reach the new, higher set point. Once the core temperature reaches this elevated point, the chills stop, and the person feels hot and flushed.
Common Causes Linked to Infection
The most frequent reason for this paradoxical sensation is an acute infection, either bacterial or viral. When pathogens invade, immune cells are activated and release endogenous pyrogens, which are small proteins known as cytokines. These cytokines signal the hypothalamus to initiate a fever.
The fever is a defense mechanism intended to create an environment unfavorable for the invading microorganisms, slowing their replication. Common illnesses like influenza, strep throat, or pneumonia frequently trigger this pyrogen-mediated response. The severity of the chills often correlates with how quickly the hypothalamic set point is being raised.
Once the immune system begins to win, or if fever-reducing medication is taken, pyrogen production decreases. This allows the hypothalamic set point to drop back toward its normal range. The body then initiates cooling mechanisms like vasodilation and sweating, which is why the fever “breaks” and the patient feels hot and sweats heavily.
Metabolic and Hormonal Triggers
While infection is the most common cause, the feeling of coldness with a hot body can also stem from non-infectious metabolic or hormonal imbalances that disrupt thermoregulation.
Hypoglycemia
Hypoglycemia, or low blood sugar, triggers a stress response in the body. When blood glucose levels drop, the body releases stress hormones like adrenaline. This hormonal surge stimulates the nervous system, resulting in symptoms such as shakiness, sweating, anxiety, and a cold or clammy feeling. This response is the body attempting to mobilize energy reserves. Hypoglycemia can occur in individuals with diabetes due to medication imbalances, or in others due to skipping meals or excessive alcohol intake.
Hormonal Fluctuations
Hormonal fluctuations, particularly during perimenopause and menopause, are another non-infectious cause of temperature dysregulation. The drop in estrogen levels affects the sensitivity of the hypothalamus, leading to vasomotor symptoms known as hot flashes. Following a hot flash, which involves intense flushing and sweating, the subsequent rapid heat loss can cause a rebound chill or shivering sensation, even if the core temperature remains high. Certain medications, including chemotherapy drugs, specific blood pressure medications, or drugs affecting the central nervous system, can also interfere with thermoregulatory pathways, producing similar sensations.
When to Seek Medical Attention
For most people, a fever with chills is a temporary response to a common infection that can be managed with rest and fluids at home. However, certain symptoms warrant prompt professional medical evaluation.
Contact a healthcare provider if an adult temperature reaches or exceeds 103°F (39.4°C), especially if it does not respond to fever-reducing medication. A persistent fever lasting longer than 48 to 72 hours without improvement should also be discussed with a doctor. Immediate medical attention is necessary if the fever and chills are accompanied by severe symptoms suggesting a more serious condition. These warning signs include:
- A stiff neck or severe headache.
- Confusion or extreme drowsiness.
- Difficulty breathing or chest pain.
- A rash that does not fade when pressed.
- Uncontrollable or violent shivering (rigors) that lasts for a prolonged period.
- Any signs of severe dehydration.