Fluctuations between feeling hot and cold, often accompanied by sweating or chills, indicate that the body’s internal temperature regulation system is being challenged. These sensations occur when the body attempts to correct an imbalance caused by external heat, internal inflammation, or a chemical change. Understanding these mechanisms reveals what the body is reacting to.
The Body’s Thermostat
The core of thermoregulation is the hypothalamus, a small region deep within the brain. It acts like a precise, involuntary thermostat, constantly monitoring blood temperature against a pre-set normal value, typically 98.6°F (37°C). To warm up, the hypothalamus triggers mechanisms to conserve and generate heat. This involves activating the sympathetic nervous system to cause vasoconstriction, narrowing blood vessels near the skin’s surface to reduce heat loss, and initiating shivering, which is rapid, involuntary muscle contraction to produce heat.
To cool the body, the hypothalamus triggers opposite responses to dissipate excess heat. It sends signals to cause vasodilation, widening blood vessels near the skin to increase blood flow and allow heat to escape. The nervous system simultaneously stimulates the sweat glands; evaporation of sweat helps carry heat away. These involuntary physiological responses maintain the narrow temperature range necessary for optimal bodily function.
Systemic Causes of Temperature Fluctuation
The most common cause of cyclical hot and cold sensations is the immune response to infection, which triggers a fever. When pathogens, such as viruses or bacteria, enter, the immune system releases chemical messengers known as pyrogens. These pyrogens travel to the hypothalamus and “reset” its thermostat to a higher temperature set point.
Because the new target temperature is higher than the current temperature, the hypothalamus interprets the body as too cold. This triggers the cold phase, where the body generates heat through shivering and chills, while minimizing heat loss through intense vasoconstriction. Once the temperature reaches this elevated set point, the sensation of cold stops, and the person feels hot as the fever is maintained. The cycle ends when the immune response subsides, pyrogens are cleared, and the hypothalamus resets the temperature to normal. The body then initiates a heat-loss response, causing the fever to “break,” typically through profuse sweating.
Hormonal and Metabolic Factors
Changes in hormone levels or metabolic processes can interfere with the hypothalamus, leading to sudden temperature shifts without infection. A key example is the vasomotor symptoms associated with perimenopause and menopause, commonly known as hot flashes. Declining and fluctuating estrogen levels disrupt hypothalamic signaling pathways, causing the thermoregulatory zone to narrow and become hypersensitive to minor temperature changes.
When the body mistakenly senses it is too warm, it rapidly triggers heat-dissipating responses, resulting in intense heat, skin flushing, and sweating. Following this heat release, the body often overshoots, leading to a subsequent sensation of cold or a chill. Another metabolic factor is hypoglycemia, or low blood sugar, which the body perceives as an emergency. In response, the adrenal glands release a surge of stress hormones, particularly epinephrine (adrenaline), to mobilize glucose reserves. This adrenaline rush causes symptoms like a rapid heartbeat, shakiness, and sudden, cold, clammy sweating.
Stress, Anxiety, and Nervous System Triggers
Temperature fluctuations can be triggered by psychological states that activate the involuntary nervous system. Acute stress, panic attacks, or severe anxiety activate the sympathetic nervous system, initiating the “fight-or-flight” response. This activation causes a rapid release of adrenaline and other stress hormones that prepare the body for immediate action.
One physiological effect of this response is the redirection of blood flow away from the skin and toward the large muscles. This shift in circulation causes the skin’s surface temperature to drop, leading to a sudden sensation of cold or chills. As the body attempts to regulate the intense metabolic activity of the stress response, it may trigger sweating, resulting in cold sweats that feel clammy. These temperature sensations are real physical symptoms, even though no infection or core temperature change has occurred.
When to Seek Medical Attention
While many instances of feeling hot and cold are linked to common, self-limiting conditions, certain symptoms warrant medical evaluation. Seek attention if a fever in an adult reaches 103°F (39.4°C) or higher, or if a lower fever persists for more than 48 hours despite home treatment. Persistent night sweats that soak clothing without a clear cause should be discussed with a doctor, as should any temperature fluctuation accompanied by unexplained weight loss. Other serious symptoms requiring immediate care include a severe headache, a stiff neck, confusion, shortness of breath, or a rash that does not fade when pressed. If temperature fluctuations interfere with daily activities, a health care provider can help determine the underlying cause and appropriate management.