Alternating sensations of feeling hot and cold usually mean your body’s internal thermostat is reacting to something, whether that’s an infection, a hormonal shift, a medication side effect, or simply a change in your environment. The list of possible triggers is long because temperature regulation sits at a crossroads of many body systems, from your thyroid and blood sugar to your nervous system and iron stores. Understanding which cause fits your pattern can help you figure out whether you need a doctor or just a different layer of clothing.
How Your Internal Thermostat Works
Your brain maintains a core temperature of roughly 37°C (98.6°F), give or take about a degree, through a feedback loop that runs continuously. Temperature sensors in your skin send information up through the spinal cord to a region in the brain called the preoptic area, which acts as the control center. When that center detects cooling, it triggers heat-generating responses like shivering, a faster heart rate, and narrowing of blood vessels near the skin to hold warmth in. When it detects warming, it does the opposite: blood vessels near the skin open up and sweating kicks in to dump heat.
This system also responds to internal chemical signals. During an infection, for instance, inflammatory molecules push the brain’s set point higher, producing fever and the chills that come with it. Hormonal changes, blood sugar swings, and certain medications can all interfere with this loop at different points, which is why so many seemingly unrelated conditions share the same symptom of feeling alternately hot and cold.
Fever and Infection
The single most common reason people suddenly feel hot and cold is a fever brought on by infection. When your immune system detects a pathogen, it releases signaling molecules that raise the brain’s temperature set point. Your body then acts as though its current temperature is too low: you shiver, your skin feels cold, and you pile on blankets. Once the fever peaks, the set point drops back down and you suddenly feel overheated, sweating to shed the excess warmth. That cycle of chills followed by flushing can repeat multiple times over the course of an illness.
The normal daily temperature swing is itself worth knowing about. Core body temperature peaks around 6 p.m. and dips to its lowest point in the early morning hours, with the daily range typically spanning about 1 to 1.5°C. Night sweats can sometimes be nothing more than an exaggerated version of this normal circadian dip, where the body overshoots its cooling and you wake up damp. When night sweats are persistent and drenching, though, they deserve medical attention because they can signal infections, cancers, or hormonal disorders.
Hormonal Shifts and Menopause
Hot flashes are the hallmark temperature disturbance of menopause, but they also happen during other hormonal transitions like the postpartum period or after surgical removal of the ovaries. The mechanism involves a group of specialized brain cells in the hypothalamus that produce three neuropeptides: kisspeptin, neurokinin B, and dynorphin. These cells, sometimes called KNDy neurons, help regulate both reproductive hormones and body temperature. When estrogen levels drop, signaling through these neurons changes in ways that appear to trigger sudden, inappropriate activation of heat-loss responses: flushing, sweating, and a racing heart, followed by chills as the body overcorrects.
Research has shown that injecting neurokinin B into healthy women induces hot flashes, strengthening the case that this signaling pathway is the trigger rather than a bystander. The finding has opened a new class of treatments: drugs that block the neurokinin B receptor are now approved specifically for menopausal hot flashes and work by interrupting the signal before it reaches the brain’s temperature-control circuits.
Hot flashes are not exclusive to women. Men undergoing androgen deprivation therapy for prostate cancer frequently experience them, and testosterone withdrawal in other contexts can produce similar episodes. The shared thread is a rapid change in sex hormone levels disrupting the same hypothalamic circuitry.
Thyroid Problems
Your thyroid gland sets the pace of your metabolism, and metabolism is basically heat production. Thyroid hormones, along with the adrenaline-driven nervous system, determine how well your body can generate warmth when it needs to. When the thyroid is underactive, the body’s heat engine runs slow. People with hypothyroidism often feel persistently cold, have cold hands and feet, and struggle to warm up in environments that others find comfortable.
Research quantifying this found that people with hypothyroidism had markedly reduced cold-induced heat generation. After their thyroid function was restored with medication, that heat generation roughly doubled. The effect is measurable and meaningful: it is not just a subjective complaint but a real physiological deficit in the ability to produce warmth on demand.
On the flip side, an overactive thyroid accelerates metabolism and heat production, leading to feeling hot, sweaty, and flushed. People with hyperthyroidism often report heat intolerance and excessive sweating even at rest. One underappreciated cause is subacute thyroiditis, an inflammation of the thyroid gland that can cause a temporary surge of thyroid hormone into the bloodstream. It sometimes presents as an unexplained fever without the classic neck pain or other thyroid symptoms, which means it gets missed.
Blood Sugar Drops
Hypoglycemia, or low blood sugar, is another trigger that catches people off guard. When blood sugar falls sharply, the body mounts a stress response: adrenaline surges, you start sweating, your heart pounds, and you may feel shaky and anxious. The sweating and flushing make you feel hot, but the accompanying peripheral changes can also make you feel clammy and cold.
A study in which insulin was used to induce low blood sugar in healthy men found that hypoglycemia reduced core body temperature by up to 2°C in some participants, with a third of subjects cooling below the normal threshold. The cooling happened because heat production dropped while sweating, blood vessel dilation, and faster breathing all increased heat loss simultaneously. For people with diabetes who take insulin or certain oral medications, these temperature swings during low blood sugar episodes are a familiar part of the experience. Eating regular meals, keeping fast-acting glucose on hand, and monitoring blood sugar can reduce the frequency and severity of these episodes.
Iron Deficiency and Feeling Cold
Iron deficiency is one of the most common nutritional shortfalls worldwide, and persistent cold intolerance is one of its less obvious symptoms. The connection runs through the thyroid: iron is required for the enzyme that converts the inactive thyroid hormone (T4) into the active form (T3). When iron is low, this conversion falters, and the result resembles a mild version of hypothyroidism with impaired ability to generate heat.
Animal research has shown this link clearly. Iron-deficient rats exposed to cold become hypothermic, and their thyroid hormone response to cold is blunted in proportion to the severity of their anemia. Human studies have confirmed the pattern: people with iron-deficiency anemia show reduced cardiovascular and thermal responses during cold exposure, and the impairment tracks with how low their iron stores are.
What makes this cause worth highlighting is that it is fixable. If you feel cold all the time and also have fatigue, pallor, or shortness of breath with exertion, a simple blood test for iron and ferritin levels can identify the problem. Iron supplementation or dietary changes can restore both iron stores and normal temperature regulation, though it takes weeks to months for levels to fully recover.
Medications That Alter Temperature Sensation
A surprisingly large number of common medications list sweating, flushing, or temperature disturbances among their side effects. Antidepressants are among the most frequently implicated. SSRIs and tricyclic antidepressants can cause excessive sweating, particularly night sweats, through their effects on the serotonin system, which is involved in thermoregulation. But the list extends far beyond antidepressants: blood pressure medications including beta-blockers, calcium channel blockers, and ACE inhibitors can all cause sweating or flushing. So can opioid pain medications, thyroid hormone supplements, corticosteroids, insulin, and even proton pump inhibitors used for acid reflux.
If your hot-and-cold episodes started around the same time you began a new medication, or if they happen primarily at night, it is worth reviewing the timing with your prescriber. In many cases, adjusting the dose or switching to a different drug within the same class resolves the problem. This is one of the most actionable causes on this list because it does not require additional testing, just a careful medication history.
Autonomic Nervous System Conditions
The autonomic nervous system is the part of your nervous system that handles things you do not consciously control: heart rate, blood pressure, digestion, and temperature regulation. When this system malfunctions, temperature control can go haywire. One of the more common autonomic disorders is postural tachycardia syndrome (POTS), in which the heart rate spikes abnormally when you stand up. People with POTS frequently report severe temperature intolerance, swinging between feeling too hot and too cold throughout the day.
A recent study of POTS patients found that over half reported a moderate to severe impact of temperature intolerance on their quality of life, affecting their ability to work, engage in leisure activities, and enjoy daily life. The problem is not just discomfort; it can be genuinely disabling, limiting what environments a person can tolerate and forcing constant adjustments to clothing and indoor climate.
Other autonomic conditions, including multiple system atrophy and pure autonomic failure, produce similar temperature dysregulation. Even people who do not meet criteria for a formal autonomic diagnosis sometimes have milder forms of dysautonomia after viral infections, concussions, or prolonged deconditioning.
Raynaud’s Phenomenon
If your hot-and-cold problem is concentrated in your fingers or toes rather than your whole body, Raynaud’s phenomenon is a likely suspect. In Raynaud’s, the small blood vessels in the extremities go into spasm in response to cold or emotional stress, dramatically reducing blood flow. The affected digits turn white as blood drains away, then blue as oxygen runs low, and finally red as blood flow returns, often with a painful, burning, throbbing sensation.
The primary form of Raynaud’s, which is not linked to any underlying disease, is quite common and mostly a nuisance. The secondary form can occur alongside autoimmune conditions like lupus or scleroderma and tends to be more severe. Management focuses on keeping the hands and feet warm, avoiding sudden temperature changes, and in more serious cases, using vasodilator medications to keep blood vessels open. People with Raynaud’s often describe the cycle as going from painfully cold and numb to painfully hot and tingling within minutes, which fits the “hot and cold” complaint precisely even though the mechanism is vascular rather than central.
How Aging Changes Temperature Regulation
As people get older, the body’s thermoregulatory machinery gradually loses some of its responsiveness. Research comparing older and younger adults during whole-body heating has found that sweating thresholds increase with age, meaning older people need to get hotter before sweating kicks in. Blood flow to the skin during heat stress is also reduced: in older adults, skin blood flow at certain body sites reached only about half to four-fifths of what younger adults achieved. These changes make it harder for older people to cool down efficiently, raising the risk of heat-related illness.
Cold tolerance also declines. Older adults tend to have lower resting metabolic rates and less brown fat, both of which reduce heat production. The combination means that an older person may feel cold in an environment that a younger person finds comfortable, and then struggle to cool down when the room warms up. This narrowing of the comfortable temperature range is a normal part of aging, but it can be amplified by medications, chronic diseases, and reduced physical fitness. Staying physically active, dressing in layers, and paying attention to hydration all help compensate for the shift.
Neurological Causes
Less commonly, hot-and-cold episodes stem from problems in the brain itself. The hypothalamus is the thermoregulatory command center, and anything that damages or irritates it can throw temperature control off. Brain tumors, traumatic brain injuries, infections like encephalitis, and congenital malformations of the nervous system can all cause sudden, unpredictable swings in body temperature. In severe cases, this manifests as what clinicians call a hypothalamic storm: abrupt episodes of high fever, sweating, rapid heart rate, and high blood pressure that come on without warning and resolve just as suddenly.
These causes are rare compared to infections or hormonal shifts, but they are worth knowing about because the temperature swings they produce can be dramatic and confusing. Someone who has had a head injury or brain surgery and subsequently develops unexplained temperature instability should have their hypothalamic function evaluated. Similarly, children with certain brain malformations may have chronic difficulties maintaining a stable temperature that require ongoing management.
Dietary and Environmental Triggers
Not every episode of feeling hot and cold signals a medical problem. Spicy foods trigger flushing and sweating through capsaicin receptors in the mouth and gut. Alcohol dilates blood vessels near the skin, producing a warm flush followed by accelerated heat loss and a subsequent chill. Caffeine can increase metabolic rate enough to cause mild sweating in sensitive individuals, especially in large doses. These dietary triggers are transient and predictable once you recognize the pattern.
Environmental factors are equally important to consider. Rapidly moving between heated indoor spaces and cold outdoor air forces your thermoregulatory system to constantly recalibrate, which can feel like alternating hot and cold sensations even though everything is working normally. High humidity impairs your ability to cool through sweating, making you feel hotter at a given temperature than you would in dry air. Physical exertion produces metabolic heat that takes time to dissipate after you stop moving, leading to a sequence of feeling overheated during activity and then chilled once you cool down. These environmental and behavioral triggers are the most common explanation for occasional hot-and-cold feelings in otherwise healthy people, and addressing them is as simple as adjusting your clothing, activity level, or indoor climate.
When Anxiety Is the Culprit
Anxiety and panic attacks activate the same fight-or-flight system that responds to physical threats. Adrenaline surges during an anxiety episode cause sweating, flushing, rapid heartbeat, and sometimes a feeling of intense heat followed by chills and goosebumps as the episode subsides. For people with anxiety disorders, these temperature fluctuations can become a daily occurrence and may feed back into the anxiety itself, creating a cycle where the physical sensations trigger more worry, which triggers more adrenaline, which triggers more temperature swings.
The distinguishing feature of anxiety-driven temperature changes is their association with psychological stress rather than with external temperature, time of day, or food intake. They tend to come with other autonomic symptoms like a churning stomach, tingling in the hands, or a sense of unreality. Cognitive behavioral therapy, regular exercise, and in some cases medication can break the cycle by reducing the frequency and intensity of the underlying adrenaline surges. If your hot-and-cold episodes happen mainly during stressful situations or periods of worry, this is a cause worth exploring with a mental health professional.