The experience of cycling rapidly between feeling hot and then cold suggests a temporary disruption in your body’s ability to maintain a stable internal temperature. This process, known as thermoregulation, is managed primarily by the hypothalamus, a small but powerful region in the brain that functions like the body’s central thermostat. Its main job is to ensure a constant core temperature, typically around 98.6°F (37°C), a state of equilibrium called homeostasis. When the body senses an internal or external temperature change, the hypothalamus initiates physiological responses designed to either generate or dissipate heat. The sudden feeling of being hot followed by a chill is often a sign that this regulatory system is reacting intensely to a trigger.
Quick Changes: Environment, Stress, and Adrenaline
Immediate and acute shifts from hot to cold sensations are often driven by rapid changes in external conditions or an intense psychological response. Moving quickly from a warm environment into a cold space can trigger peripheral vasoconstriction, where blood vessels near the skin narrow to shunt warm blood toward the body’s core. This helps conserve heat but can briefly leave the skin feeling cool or chilled. Conversely, exposure to intense heat can prompt immediate vasodilation, causing blood vessels to widen and bring more heat to the skin’s surface for dissipation, which feels like a sudden wave of warmth.
The body’s acute stress response, commonly known as “fight or flight,” also creates these rapid temperature fluctuations through the release of hormones like adrenaline. When a high-stress event occurs, the sympathetic nervous system is instantly activated, causing blood flow to be redirected to large muscle groups. This redirection, combined with an increase in heart rate and metabolism, can temporarily cause a feeling of intense, internal heat or flushing.
This adrenaline-fueled surge of heat prompts the body’s cooling mechanisms to activate immediately. The sudden onset of sweating is one of the most effective ways the body sheds heat, as the evaporation of moisture from the skin rapidly cools the surface. Once the initial heat from the adrenaline rush is released, the remaining moisture on the skin can quickly make you feel chilled or cold. These quick, reactive temperature shifts are typically brief and resolve once the trigger has passed.
Temperature Cycles Caused by Infection and Immunity
One of the most common causes of this hot-then-cold cycle is the body’s intentional immune response to an infection, manifesting as a fever. When pathogens enter the body, immune cells release signaling molecules called pyrogens into the bloodstream. These pyrogens travel to the hypothalamus and effectively “reset” the thermostat to a higher temperature set point.
The feeling of intense cold and uncontrollable shivering, known as the chills, occurs when the body’s core temperature is still at its normal level but is now below the hypothalamus’s new, higher set point. The body interprets this discrepancy as being dangerously cold, initiating heat-generating mechanisms like shivering and extreme peripheral vasoconstriction to rapidly raise the temperature. Once the body reaches this elevated temperature, the person registers the fever as feeling hot.
The cycle reverses when the pyrogens are cleared from circulation. The hypothalamus resets the temperature set point back down, and the body suddenly finds itself overheated relative to the new target. To dissipate this excess heat rapidly, the body triggers vigorous vasodilation and profuse sweating, a process often described as the fever “breaking.” The speedy evaporation of this sweat then cools the skin effectively, completing the cycle from hot back to cold.
Systemic Causes: Hormones and Metabolism
Long-term or frequently recurring temperature shifts can indicate a systemic regulatory issue involving hormones or metabolism. The thyroid gland controls the metabolic rate and directly influences heat production. An overactive thyroid, or hyperthyroidism, accelerates metabolism, causing the body to constantly generate excess heat, leading to chronic feelings of being too hot and sweating excessively. Conversely, an underactive thyroid, or hypothyroidism, slows metabolism, resulting in reduced heat production and a persistent feeling of coldness.
Fluctuations in sex hormones, particularly estrogen, are a major systemic cause of these temperature swings, most notably in perimenopause and menopause. The decline of estrogen is thought to destabilize the thermoregulatory center in the hypothalamus, narrowing the thermoneutral zone. Even a tiny rise in core temperature can inappropriately activate the heat-dissipation response, resulting in a hot flash—a sudden wave of heat, flushing, and sweating. This intense heat loss is frequently followed by a cold sensation as the body overshoots the cooling process.
Blood sugar regulation issues, such as hypoglycemia (low blood glucose), also trigger an internal temperature shift. When blood sugar drops, the body releases counter-regulatory hormones like adrenaline, which serves to raise glucose levels and activates the sympathetic nervous system. This adrenaline release causes symptoms like trembling, anxiety, and the rapid onset of sweating. The resulting cold, clammy sweat is the definitive feature of a hypoglycemic episode, creating a sudden shift from an internal feeling of unease and heat to a sensation of external coldness.
Knowing When to Consult a Doctor
While isolated or brief episodes of feeling hot then cold are often benign, certain accompanying symptoms warrant consultation with a healthcare provider. You should seek medical advice if your temperature fluctuations are persistent, severe, or interfere with your daily life. A key warning sign is any fluctuation that is accompanied by an unexplained, significant weight loss or profound, chronic fatigue. Fevers that are high grade, such as above 103°F (39.4°C), or that last for more than 72 hours should be medically evaluated. Persistent night sweats that soak your clothing or bedding, or temperature changes paired with severe pain or confusion, require prompt attention.