The sensation of rapidly alternating between feeling hot and cold, often described as temperature swings or chills, is a common experience. This oscillating feeling is a direct result of the body’s system for maintaining a stable internal temperature, a process known as thermoregulation. When the body perceives a threat to this stability, it rapidly deploys mechanisms to either generate or release heat, creating the uncomfortable sensation of being too hot one moment and shivery the next.
How the Body Regulates Temperature
The core of the body’s temperature control system is the hypothalamus, a small region in the brain that acts like a thermostat. The hypothalamus maintains the core body temperature within a narrow range, typically around 37 degrees Celsius (98.6 degrees Fahrenheit), known as the set point. It receives continuous input from temperature sensors, called thermoreceptors, located centrally in the viscera and spinal cord, and peripherally in the skin.
When the body needs to cool down, the hypothalamus activates heat-dissipating responses. This includes vasodilation, where blood vessels near the skin surface widen to increase blood flow, allowing excess heat to radiate away. Sweat glands are simultaneously activated, and as the moisture evaporates from the skin, it provides a cooling effect.
Conversely, if the internal temperature drops below the set point, the hypothalamus triggers mechanisms to conserve and generate heat. This involves vasoconstriction, where blood vessels narrow to shunt warm blood away from the skin and toward the core organs, reducing heat loss. If this is insufficient, the body initiates shivering, which involves rapid, involuntary muscle contractions that generate heat as a byproduct of increased metabolic activity. The alternating feeling of hot and cold is the experience of these opposing physiological actions occurring sequentially.
Everyday Triggers for Temperature Swings
Many instances of sudden temperature changes stem from simple shifts in the environment or lifestyle. Moving abruptly from a cold, air-conditioned space into high outdoor heat can confuse the body’s peripheral sensors. The body overreacts to the sudden environmental shift, leading to a brief period of discomfort as the hypothalamus recalibrates.
Physical exertion provides another common trigger, particularly during the post-exercise cool-down period. Intense activity elevates the core body temperature, triggering sweating and vasodilation to release heat. Once the exercise stops, heat production drops quickly, but the body’s cooling mechanisms may temporarily overcompensate, leaving a person feeling suddenly chilled and clammy.
Emotional states, such as anxiety or stress, can initiate rapid temperature fluctuations through the body’s “fight or flight” response. The release of stress hormones, like adrenaline, increases heart rate and metabolic activity, creating a sensation of warmth or sweating. Once the emotional surge subsides, the body’s attempt to return to its baseline can lead to a sudden cold or clammy feeling. Consumption of certain substances also acts as a trigger; for example, capsaicin in spicy foods activates heat-sensitive receptors, initiating cooling responses like sweating. Alcohol causes peripheral vasodilation, making a person feel warm, but this leads to faster heat loss and subsequent chills.
Internal Conditions and Hormonal Influences
The most persistent temperature swings often occur when an internal condition alters the hypothalamic set point or its sensitivity. A prominent example is the fever response to an infection, which is a defense mechanism. Pyrogens, which are fever-inducing substances released by immune cells, signal the hypothalamus to raise the core temperature set point to a higher level.
The feeling of intense cold and shivering, or “the chills,” happens when the actual body temperature is below this newly elevated set point. The body responds by initiating heat production through vasoconstriction and shivering, attempting to reach the new, higher temperature. Once the infection subsides and the pyrogens are cleared, the set point returns to normal, prompting the body to shed excess heat rapidly through sweating and vasodilation, which is the “hot” phase.
Hormonal shifts, particularly those associated with menopause, also cause thermoregulatory instability, resulting in hot flashes. The decline in estrogen levels can destabilize the control center in the hypothalamus, narrowing the range of temperature tolerance. This makes the body hypersensitive to small changes in core temperature, leading to a sudden activation of heat loss mechanisms, characterized by intense heat, flushing, and sweating. The subsequent rapid heat loss often results in a feeling of cold or a chill once the flush passes.
Other internal factors, such as thyroid conditions, can affect metabolic rate and heat production. Hyperthyroidism, or an overactive thyroid, increases the body’s basal metabolic rate, which can lead to a persistent feeling of being too warm. Certain medications, including antidepressants and blood pressure drugs, can interfere with the body’s ability to sweat or regulate blood flow to the skin. Diuretics, or water pills, can also cause dehydration and electrolyte imbalances that impair the sweating response, indirectly affecting thermoregulation.
When to Consult a Healthcare Professional
While occasional temperature swings are harmless and linked to everyday factors, they can signal an underlying health issue when they become frequent or severe. A consultation is warranted if the alternating hot and cold sensations are persistent and occur without a clear trigger, such as exercise or spicy food. This is especially true if the swings are accompanied by other symptoms, including unexplained weight loss, chronic fatigue, or severe pain.
Any temperature fluctuation that involves a high fever, confusion, or a sudden change in mental status requires prompt medical attention. If a temperature swing is a new side effect following the start of a medication, or if it interferes with daily life or sleep, speaking with a healthcare provider can help determine if an adjustment is necessary.