What Are Chills a Sign Of? Causes and When to Worry

Chills are your body’s rapid-fire muscle contractions designed to generate heat, and they can signal anything from a straightforward viral infection to a serious bacterial invasion of the bloodstream. Most of the time, chills accompany a rising fever as your brain temporarily resets its internal thermostat upward, but the same shivering response can be triggered by cold exposure, hormonal shifts, certain medications, and even intense emotional experiences. The range of possible causes is wide enough that the context surrounding the chills matters as much as the chills themselves.

How Your Body Produces Chills

The shivering you feel during a chill is not random. It starts in a temperature-control center deep in the brain, specifically in the preoptic area of the hypothalamus. Under normal conditions, this region keeps your core temperature locked in a narrow band. When something disrupts that set point, whether it’s cold air hitting your skin or a fever-producing signal from an infection, a cascade of nerve signals fires downward through the brainstem to your skeletal muscles, commanding them to contract rapidly and rhythmically. Those involuntary contractions are what you experience as shivering, and their purpose is to churn out metabolic heat.

When the trigger is an infection rather than cold weather, the pathway is slightly different. Immune cells detect the invader and release signaling molecules called pyrogenic cytokines. These cytokines prompt specialized cells in the hypothalamus to produce prostaglandin E2, which effectively raises the brain’s temperature set point from its normal level to a higher, “febrile” target.¹ Your body then behaves as though it is too cold relative to that new, higher target. Blood vessels near the skin constrict to conserve heat, and shivering kicks in to produce more. The result is the paradox many people find confusing: you feel freezing cold even though your temperature is actually climbing.

Research on the neural circuitry confirms that the shivering response during fever uses the same descending brain pathways as the shivering response to genuinely cold surroundings. Both are driven by excitatory signals passing through the dorsomedial hypothalamus and the rostral raphe pallidus in the brainstem.² This shared wiring explains why a chill feels the same whether you stepped into a walk-in freezer or are coming down with the flu.

Infections Are the Most Common Cause

For most people, the first association with chills is “I’m getting sick,” and that instinct is usually right. Viral infections like influenza are among the most frequent triggers. During acute influenza, the body releases interleukin-6 and other inflammatory cytokines, and higher levels of these molecules correlate with both worse symptoms and higher fevers.³ The chills you feel at the onset of the flu are essentially the opening salvo of your immune system ramping up that inflammatory response.

Bacterial infections can produce even more dramatic chills. Urinary tract infections, pneumonia, and kidney infections are common culprits, but any bacterial infection that reaches the bloodstream (bacteremia) can trigger severe, shaking rigors. These aren’t just mild shivering; they’re whole-body episodes that are hard to suppress. A systematic review found that shaking chills are a highly specific predictor of bacteremia, meaning that when someone has them, the odds that bacteria are actually in the blood go up substantially.⁴ One prospective study put the adjusted odds of a positive blood culture at roughly three to four times higher in patients who reported shaking chills compared with those who did not.⁵

Malaria offers perhaps the most textbook example of infection-driven chills. In Plasmodium vivax malaria, patients experience sharp “paroxysms,” episodes of high fever accompanied by violent chills and rigors that recur on a predictable 48-hour cycle. Research has shown that tumor necrosis factor (TNF) levels in the blood closely track the rise and fall of temperature during these paroxysms, with the TNF spike typically preceding the fever by about half an hour to an hour.⁶ Malaria is not a common concern in most high-income countries, but for travelers returning from endemic regions, cyclic fevers with rigors should raise an immediate red flag.

Chills Without Infection

Not every episode of chills means you’re fighting off a pathogen. Cold exposure is the most obvious non-infectious cause. When your skin temperature drops, thermoreceptors send signals to the hypothalamus, which initiates the same shivering response described above. The colder the environment and the less insulation you have, the more intense the shivering becomes. Prolonged or severe cold exposure can push someone toward hypothermia, at which point shivering may actually stop as the body’s reserves are depleted.

Physical exhaustion can make you more vulnerable to cold-related chills. After several days of intense exercise, the body’s ability to constrict blood vessels in response to cold becomes impaired, even though the shivering response itself remains intact.⁷ This means that after a grueling workout or multi-day athletic event, you can lose body heat faster than usual even in conditions that wouldn’t normally bother you. The chills that follow aren’t a sign of illness; they’re a sign that your thermoregulatory system is temporarily running on fumes.

Low blood sugar (hypoglycemia) is another underappreciated trigger. When glucose levels drop, the body mounts a stress response that includes adrenaline release, trembling, and chills. People with diabetes who take insulin or certain oral medications may recognize this pattern, though it can happen to anyone who goes too long without eating, particularly after vigorous activity.

Hormonal and Thyroid-Related Chills

Thyroid hormones play a central role in regulating your metabolic rate and, by extension, how much heat your body produces at rest. In hypothyroidism, reduced thyroid hormone levels decrease cold-induced thermogenesis, which is your body’s ability to crank up heat production when exposed to cool temperatures. Research has confirmed that even moderate hypothyroidism reduces this cold-adaptive response, and that proper thyroid hormone replacement restores it.⁸ If you find yourself perpetually chilly in rooms where everyone else seems comfortable, an underactive thyroid is worth investigating.

Menopause introduces a different kind of thermoregulatory disruption. Hot flashes are the headline symptom, but the full cycle often includes chills as well. A hot flash is a burst of vasodilation and sweating triggered by a narrowed thermoneutral zone in the hypothalamus, a consequence of declining estrogen levels.⁹ Once the flash passes, the rapid heat loss from flushed, sweaty skin can overshoot, dropping skin temperature enough to trigger chills and shivering. These episodes typically last one to five minutes and can include sensations of anxiety alongside the temperature swings.¹⁰ The chill at the tail end of a hot flash is not a separate problem; it’s the body overcorrecting after the flush of heat loss.

Medications, Anesthesia, and Substance Withdrawal

Post-surgical shivering is common enough that anesthesiologists consider it a routine complication. General and regional anesthesia impair the body’s thermoregulation, often allowing core temperature to drift downward during a procedure. Shivering after waking up is typically a response to that drop. But it also occurs in patients whose temperature never fell below normal, suggesting that other mechanisms are at play, including pain signaling and acute withdrawal from short-acting opioids used during the surgery.¹¹

Opioid withdrawal more broadly is one of the most intense non-infectious causes of chills. When someone who has developed physical dependence on opioids stops using them abruptly or reduces the dose too quickly, withdrawal symptoms emerge. Chills, goosebumps, sweating, muscle aches, and gastrointestinal distress are hallmarks. The severity scales with the degree and duration of dependence. Alcohol withdrawal can produce similar autonomic instability, including chills, tremors, and sweating, and in severe cases can be medically dangerous.

Certain medications can cause chills as a side effect outside of any withdrawal scenario. Some chemotherapy drugs, biologic therapies used for autoimmune diseases, and even certain antibiotics can trigger chills during or shortly after infusion. These reactions are typically related to the drug prompting cytokine release, which mimics the same fever pathway the body uses during infection. If you consistently develop chills after receiving a specific medication, your prescriber can often adjust the infusion rate or add a premedication to blunt the response.

Emotional and Psychological Triggers

Chills don’t always have a physical origin. Panic attacks can produce a cluster of somatic symptoms that include trembling, sweating, and chills or hot flashes. Research on the symptom structure of panic disorder has identified chills and hot flashes as part of a mixed somatic factor that appears alongside sweating, nausea, and dizziness.¹² These aren’t imagined sensations; they’re real autonomic nervous system events driven by the same fight-or-flight circuitry that prepares the body for perceived danger. Adrenaline redirects blood flow, skin vessels constrict, and goosebumps and chills follow.

On the more pleasant side, strong emotional experiences can also trigger chills. The phenomenon known as “frisson,” those spine-tingling shivers you get from a moving piece of music, a powerful speech, or a breathtaking view, involves the brain’s dopamine reward system. Neuroimaging research has traced musical frisson to activity in the caudate nucleus during the anticipatory buildup and the nucleus accumbens during the peak emotional moment, with the strength of the experience linked to how well-connected a person’s auditory processing areas are to their emotional and reward circuits.¹³ Not everyone experiences frisson with the same intensity, and some people rarely experience it at all, which appears to be partly a matter of individual neural wiring.

Chills in Children Versus Adults

The diagnostic significance of chills shifts depending on age. In children up to 17 years old, the combination of fever, chills, and cough is a strong predictor of influenza virus infection, with fever playing a prominent role. In adults, chills and cough remain important predictors, but fever drops out as a key indicator. One large validation study found that the combination of chills and cough without fever was highly specific for influenza in adults, with about 96% specificity, though sensitivity was low at around 30%.¹⁴

The practical implication: if your child has chills with a fever during flu season, influenza is a leading suspect. If you’re an adult who develops chills and a dry cough but your temperature reads normal on the thermometer, influenza is still plausible. The reason likely has to do with differences in immune response; children tend to mount a stronger innate fever response than adults, so fever is more reliably present in younger patients.

Older adults face a different concern. They’re more likely to have blunted fever responses, meaning a serious infection can be underway with only a low-grade temperature or none at all. Chills or rigors in an older adult, even without an impressively high fever, deserve prompt medical attention. Bacteremia is more common in this population, and age over 75 has been identified as an independent predictor of positive blood cultures in outpatient settings.

When Chills Are a Red Flag

The intensity and context of chills make a big difference. Mild chilliness when you’re underdressed or sitting in a drafty room is unremarkable. But severe, shaking rigors, the kind where your teeth chatter and your whole body shakes uncontrollably, warrant closer attention, particularly if they occur alongside other signs of systemic illness.

The strongest clinical concern attached to shaking chills is bacteremia. A multicenter observational study found that shaking chills had a specificity above 90% for predicting bacteremia in outpatients, and patients who reported them had roughly three times the odds of a positive blood culture compared to those who did not.¹⁵ That said, the sensitivity was not high, meaning plenty of patients with bacteremia did not report shaking chills. So the absence of rigors does not rule out a bloodstream infection.

Situations where chills should prompt you to seek medical evaluation sooner rather than later include:

• High or persistent fever: Chills paired with a temperature above 103°F (39.4°C) in adults, or any fever in an infant under three months, needs prompt attention.
• Shaking rigors: Intense, whole-body shaking episodes that last several minutes suggest the body is mounting a significant immune response and may indicate a bloodstream infection.
• Recent surgery or hospitalization: Post-operative chills with fever can indicate a surgical site infection or other hospital-acquired complication.
• Immune compromise: If you’re undergoing chemotherapy, taking immunosuppressant medications, or living with HIV, chills with fever can signal infections that progress rapidly.
• Travel to endemic areas: Cyclic fevers with rigors after travel to regions where malaria is present need urgent evaluation, ideally including a blood smear.
• Accompanying confusion or low blood pressure: Chills combined with altered mental status, rapid heartbeat, or a drop in blood pressure may indicate sepsis, which is a medical emergency.

Common Misconceptions About Chills

One persistent myth is that chills themselves make you sicker, or that shivering is something you should try to suppress with heavy blankets and hot drinks. In reality, fever-associated chills are part of the body’s defense mechanism. Raising core temperature can inhibit the growth of some pathogens and enhances certain immune functions. Piling on blankets during a rigor makes you feel better in the moment, but it won’t significantly change the course of the illness. Conversely, aggressively cooling someone who is shivering with fever (cold baths, ice packs) tends to increase shivering and discomfort without meaningfully lowering core temperature, because the hypothalamic set point is still elevated.

Another misconception is that “chills without fever” is always benign. While it’s true that many non-fever causes of chills (cold exposure, anxiety, low blood sugar) are not dangerous, some infections, particularly in older adults or immunocompromised individuals, produce chills without an obvious temperature spike. The fever may simply be delayed, suppressed by medications like NSAIDs, or blunted by age-related changes in immune function. Chills that feel “infectious” in character, especially if they’re accompanied by fatigue, body aches, or a general sense of being unwell, still warrant monitoring even if the thermometer reads normal initially.

Finally, people sometimes confuse chills with cold intolerance. Cold intolerance is a chronic condition where you consistently feel cold in environments others find comfortable, and it’s often linked to thyroid dysfunction, anemia, or low body weight. Chills, by contrast, are episodic events involving involuntary muscle contractions. The two can overlap (someone with hypothyroidism can also get an infection and develop chills), but they’re distinct phenomena with different underlying causes. Addressing chronic cold intolerance means investigating metabolic or circulatory issues, while addressing acute chills means figuring out what’s triggering that specific episode.

Musical Frisson and the Neuroscience of Pleasant Chills

Not all chills are unwelcome. The tingling shivers that run down your spine during an unexpectedly beautiful passage of music, or while watching a film scene that lands perfectly, are a well-documented phenomenon that researchers call frisson. Unlike pathological chills, frisson involves piloerection (goosebumps), a brief shiver, and often a rush of pleasurable emotion, all without any change in core body temperature.

The neuroscience behind frisson points to the dopamine reward system. Brain imaging studies have shown that the anticipatory phase, the moment just before the musical peak that gives you shivers, activates the caudate nucleus, while the peak moment itself lights up the nucleus accumbens. These are the same brain regions involved in other rewarding experiences. The degree to which someone experiences frisson appears related to the structural connectivity between their auditory cortex and their emotional and reward-processing regions.¹³ People with stronger white-matter connections between these areas seem to experience frisson more readily and more intensely. Personality research has also linked frisson to the trait of “openness to experience,” though the neural connectivity finding suggests the phenomenon runs deeper than just being a music lover. Some brains are simply wired to translate auditory beauty into a physical shiver.