Feeling hot and then suddenly cold usually means your body is correcting itself, not that something is broken. The brain runs a thermostat, and when it overshoots in one direction it pushes back the other way, often with sweat that leaves you chilled. The same swing can come from very different sources, from a cold or a hormone shift to a racing nervous system, so the pattern and timing matter more than the feeling itself.
How Your Body Swings From Hot to Cold
A small region at the base of the brain acts as your body’s thermostat.1PubMed Central. A hypothalamic circuit that controls body temperature One group of its nerve cells works to lower body temperature, while another raises it by burning more energy and increasing activity.2PubMed Central. A hypothalamic circuit that controls body temperature When the cooling side is switched off, temperature can climb to fever levels, and when the warming side is switched off, temperature drops.3PubMed Central. A hypothalamic circuit that controls body temperature Hot and cold feelings are two halves of one control system, not two separate problems. Unlike a home thermostat, your body’s setting can move, which is why you can feel cold while actually running warm.
When the brain decides you’re too warm, it widens blood vessels in the skin, which causes flushing, and then turns on sweating.4Harvard Health. Hot flashes in men: An update Sweat soaked into clothing cools the body as it evaporates, and moving air speeds that up and can drop body temperature substantially.5Textile Progress. Heat, moisture and air transport through clothing textiles
A typical swing starts with warmth over the face and chest, then sweat, then a chill minutes later as the wet skin cools. The sequence can repeat several times in a day or night.
Shivering and sweating are both corrections. Shivering is the body making heat: muscles contract rapidly to burn energy, so a chill is an active response, not proof that the air is cold. Goosebumps and pale, cool hands and feet come from skin blood vessels narrowing to hold heat in, the opposite of the flushing that comes with sweating. The body acts in proportion to how far it is from its target, so a big heat surge calls for a big cooling response, and the cooling can overshoot.
Fever and Infection
During a fever, the body’s controls for flushing and sweating switch on at a higher temperature than normal.6Journal of Clinical Investigation. Circulation and Respiration During an Episode of Chill and Fever in Man The brain’s set point has been reset upward, rather than the body simply overheating.7Journal of Clinical Investigation. Circulation and Respiration During an Episode of Chill and Fever in Man So at the start you feel cold and may shiver even as your temperature rises, and when the fever breaks you feel hot and sweat it off.
Once the brain raises its target, your normal temperature is suddenly below the goal, and you shiver until you catch up. When the target drops back, whether from medicine or the infection easing, you sit above it, so you flush and sweat.
To tell infection chills from other causes, check your temperature with a thermometer during both the cold phase and the hot phase. A reading of 100.4°F (38°C) or higher points to fever. Body aches, a sore throat, a cough, or burning when you urinate suggest an infection. Swings without a raised reading point toward the other causes in this article.
Fever appears to help fight infection partly by stressing the germs more than it stresses you.8Evolution, Medicine, and Public Health. Let fever do its job: The meaning of fever in the pandemic era Bringing a fever down may make you feel better without necessarily helping you recover faster.9Evolution, Medicine, and Public Health. Let fever do its job: The meaning of fever in the pandemic era But fever also speeds the heart and raises the body’s oxygen needs.10PubMed Central. Temperature control in sepsis Very high temperatures damage cells directly, starting around 41°C (about 106°F).11PubMed Central. Temperature control in sepsis A mild fever in a healthy adult can often be ridden out, but a very high one needs treatment.
For comfort, use light layers you can add and remove rather than heavy blankets. Drink fluids, since sweating loses water. Fever reducers can ease misery if you follow the label dose. Change out of sweat-soaked clothes so you avoid the chill described earlier.
Hot Flashes From Menopause and Low Testosterone
A hot flash is a sudden wave of heat with flushing and sweating that comes from the brain’s temperature center.12Harvard Health. Hot flashes in men: An update To counter the rising skin temperature, the body quickly turns the warm flush into a cold, clammy sweat.13Harvard Health. Hot flashes in men: An update No substance found in the blood during hot flashes has been shown to trigger them,14Canadian Journal of Physiology and Pharmacology / NRC Research Press. Thermoregulatory physiology of menopausal hot flashes: a review so there is no simple blood test that confirms one. The pattern of symptoms is the guide.
Most hot flashes are short, often lasting a few minutes, and feel like heat rising through the chest, neck, and face. A racing heartbeat or a brief sense of unease can come with one, which is why some people mistake them for anxiety.
A fever raises the brain’s target so your temperature truly climbs and stays up for hours, while a hot flash is a brief overreaction that passes. With a hot flash a thermometer reading is usually normal, so a normal reading with repeated flushing fits hormones better than infection. Sore throat, cough, and body aches are usually absent too.
In postmenopausal women, most hot flashes are preceded by a small rise in core body temperature.15PubMed. Core body temperature and circadian rhythm of hot flashes in menopausal women Anything that warms you, like a hot room, a hot drink, or exercise, can tip you into one.16PubMed. Core body temperature and circadian rhythm of hot flashes in menopausal women They also follow a daily rhythm, peaking around 6:30 in the evening.17PubMed. Core body temperature and circadian rhythm of hot flashes in menopausal women
Keep the bedroom cool and use layered bedding. Carry a fan or wear breathable fabrics during the evening peak. Notice personal triggers such as alcohol, spicy food, or hot drinks. If flashes disrupt sleep or work, talk with a doctor about treatments.
Men get them too. About 70% to 80% of men treated with hormone-lowering therapy for prostate cancer get hot flashes.18Harvard Health. Hot flashes in men: An update Low testosterone is the cause, acting through the same brain temperature center.19Harvard Health. Hot flashes in men: An update
Anxiety and Panic
Hot and cold flashes are a recognized part of panic attacks, alongside palpitations, tremor, and restlessness.20Archives of General Psychiatry. Noradrenergic Function in Panic Anxiety: Effects of Yohimbine in Healthy Subjects and Patients With Agoraphobia and Panic Disorder People with panic disorder appear more sensitive to surges of the body’s fight-or-flight chemicals.21Archives of General Psychiatry. Noradrenergic Function in Panic Anxiety: Effects of Yohimbine in Healthy Subjects and Patients With Agoraphobia and Panic Disorder Withdrawal from alcohol, opioids, or other drugs also commonly causes hot and cold flushes with sweating and anxiety.22Valley Hope. Common Addiction Withdrawal Symptoms and How to Prevent Them
An anxiety-driven episode often comes with a pounding heart, shaking, or a sense of dread. It peaks within minutes and fades rather than lasting all day, and a thermometer stays normal. Slow breathing can shorten an episode, and repeated attacks deserve treatment.
Caffeine, poor sleep, and stimulant medicines can push the nervous system toward the same surge, making an episode more likely. A swing can begin with a worrying thought or with a body sensation, like a skipped heartbeat, that you then read as danger, which feeds the surge.
An overactive thyroid can mimic anxiety, as covered next. A first episode with chest pain should be checked, not assumed to be panic.
Thyroid and Nervous System Conditions
The thyroid gland sets how much energy your body burns and how it handles heat.23Mayfield Clinic. Always Cold or Sweating? Your Thyroid & Body Temperature An overactive thyroid can make you sweaty, anxious, and lose weight without trying, while an underactive one leaves you cold and sluggish.24Mayfield Clinic. Always Cold or Sweating? Your Thyroid & Body Temperature Some people have flares of overactivity with flushing, sweating or chills, palpitations, and tremor.25PubMed. Intermittent hyperthyreosis — a heat stress syndrome If swings come with weight or energy changes, a simple blood test for thyroid hormone is worth asking about. It is a routine blood draw, usually needing no special preparation, and the results separate an overactive thyroid from an underactive one.
Thyroid heat intolerance tends to be steady, a feeling of being warm most of the time, rather than coming in short waves. Weight loss despite normal eating, a fast pulse, and tremor point more toward thyroid than hormonal flashes. An underactive thyroid usually brings constant coldness with tiredness and dry skin, not alternating heat and sweat.
Dysautonomia (including POTS) is a problem with the automatic nervous system, which also controls body temperature.26PoTS UK. Temperature Regulation Many people with it can’t tolerate heat or cold.27Dysautonomia Support Network. Thermoregulation Heat widens blood vessels and raises heart rate, while low blood volume can cause cold.28PoTS UK. Temperature Regulation29Dysautonomia Support Network. Thermoregulation POTS often brings flushing, lightheadedness, and changes in sweating.30Nursing Made Incredibly Easy!. Dysautonomia: Getting a handle on POTS
Multiple sclerosis (MS) is another possibility. About 60% to 80% of people with MS find their symptoms temporarily worsen when body temperature rises or falls.31PubMed Central. Temperature sensitivity in multiple sclerosis: An overview of its impact on sensory and cognitive symptoms Temperature changes slow signals in damaged nerves.32PubMed Central. Temperature sensitivity in multiple sclerosis: An overview of its impact on sensory and cognitive symptoms
Everyday Triggers After Exercise and During Sleep
During exercise your muscles generate heat and you sweat heavily to shed it, so you are wet and warm when you stop. Once you stop moving, heat production falls quickly while sweat on your skin keeps cooling you, and a chill sets in. After a hard workout, the body waits until it’s colder before it starts conserving heat and shivering.33RunnersConnect. Chills After Working Out: Why and When to Worry | RunnersConnect It is worse outdoors in wind or in air conditioning, because moving air speeds evaporation. Change into dry clothes and add a layer soon after exercise.
At night, bedroom temperature strongly affects body temperature during sleep.34PubMed. Sweating responses and body temperatures during nocturnal sleep in humans Core temperature naturally drops as you fall asleep and bottoms out in the early morning. Heavy blankets or a warm room can interfere with that drop and trigger sweating. Sweating is strongest in deep sleep and weakest in dream sleep,35PubMed. Sweating responses and body temperatures during nocturnal sleep in humans so you can wake soaked and then cold as sleep lightens and the damp skin loses heat.
To break a night sweat-and-chill cycle, set the room cooler rather than piling on blankets, and use moisture-wicking sleepwear. Keep a dry shirt by the bed. Persistent drenching night sweats with weight loss need a doctor.
When Hot and Cold Swings Are an Emergency
In heat stroke, the body’s cooling fails, sweating may stop, and body temperature can climb to 106°F or higher within 10 to 15 minutes.36Centers for Disease Control and Prevention (CDC) / NIOSH. Heat-related Illnesses It can cause permanent disability or death without emergency treatment.37Centers for Disease Control and Prevention (CDC) / NIOSH. Heat-related Illnesses Adults over 60 lose some ability to shed heat and face the highest risk during heat waves.38PubMed Central. Aging and Thermoregulatory Control: The Clinical Implications of Exercising under Heat Stress in Older Individuals Call emergency services if someone in the heat is very hot, confused, or collapses, whether or not they are still sweating.
While waiting for help, move the person to shade or indoors and remove extra clothing. Cool the body quickly with cool water on the skin, wet cloths, fanning, or ice packs on the neck, armpits, and groin. Don’t give fluids if the person is confused or can’t swallow safely, and don’t leave them alone.
Other red flags need same-day care: a fever above 103°F (39.4°C) or one lasting more than three days; shaking chills with confusion, fast breathing, or low blood pressure, which can signal sepsis and need emergency care right away; chest pain or fainting with flushing; and a stiff neck, severe headache, or rash with fever.
When you see a doctor, say how often the swings happen and at what times of day, and bring any thermometer readings from episodes. Mention new medicines, recent illness, or stopping alcohol or drugs, along with other changes like weight loss, a racing heart, or dizziness.