Chills are your body’s way of generating heat through rapid, involuntary muscle contractions. Whether triggered by cold air, a rising fever, a powerful piece of music, or a drop in blood sugar, the underlying mechanism is similar: your brain detects a gap between your current body temperature and where it “should” be, then activates muscles to close that gap. But temperature isn’t the only trigger. Chills can also stem from emotional responses, medical conditions, and hormonal shifts.
How Your Body Produces Chills
The shivering you feel during chills is coordinated by the hypothalamus, a small region at the base of your brain that acts as your internal thermostat. When it senses that your core temperature is too low, it triggers rapid cycles of muscle contraction and relaxation. These contractions are small, typically only 5 to 16 percent of a muscle’s maximum force in the trunk and even less in the arms and legs. But they’re remarkably effective at producing warmth, capable of boosting your heat output to roughly five times above resting levels.
Your body is strategic about where it shivers. About 71 percent of the heat generated during chills comes from the large muscles of your trunk (chest, back, and abdomen), with another 21 percent from the thigh muscles. The arms and lower legs contribute only about 8 percent. This makes sense: your core houses your vital organs, and your limbs lose heat quickly because of their high surface area. Concentrating the shivering in your torso keeps the warmth where it matters most.
The muscle fibers recruited during shivering are the slow-twitch, fatigue-resistant type. Your body favors these because they can sustain low-level contractions for a long time without exhausting themselves or cutting off their own blood supply. It’s a marathon strategy, not a sprint.
Fever Chills: Feeling Cold While Getting Hotter
One of the most confusing experiences with chills is shivering under a pile of blankets while running a fever. This happens because of a reset in your brain’s thermostat. During an infection, your immune system releases signaling molecules called cytokines. These molecules reach the hypothalamus either by crossing into the brain through the bloodstream or by stimulating the vagus nerve, which runs from your gut to your brainstem.
Once those signals arrive, the hypothalamus raises its temperature set point, sometimes from the normal 98.6°F to 101°F, 102°F, or higher. Your actual body temperature hasn’t caught up yet, so your brain perceives a gap. As far as your thermostat is concerned, you’re too cold. It responds the same way it would on a freezing day: triggering shivering, constricting blood vessels near your skin to trap heat inside, and driving you to curl up and seek warmth. You feel freezing even though your temperature is climbing. Once your core temperature reaches the new set point, the chills stop, and you may start sweating instead as the fever breaks and your thermostat resets back to normal.
Emotional and Musical Chills
Not all chills are about temperature. That wave of goosebumps during a powerful song, a moving speech, or an awe-inspiring moment is called frisson. Research from McGill University confirmed that these “musical chills” involve a release of dopamine, the same brain chemical associated with food, sex, and other rewards. Skin conductance, heart rate, breathing, and skin temperature all shift measurably during these peak emotional moments.
Two separate brain circuits drive the experience. One connects to cognitive and motor systems and is involved in anticipation (the buildup before the musical climax you know is coming). The other connects to the limbic system, the emotional core of your brain, and fires during the experience itself. The fact that emotional chills tap into the same ancient reward circuitry as basic survival drives helps explain why they feel so physically intense despite having nothing to do with being cold or sick.
Chills Without Fever or Cold
Several conditions can cause chills even when you’re not fighting an infection or sitting in a cold room:
- Low blood sugar (hypoglycemia): When blood glucose drops too low, your body releases stress hormones that can trigger shaking and chills. This is especially common in people managing diabetes with insulin.
- Panic attacks and adrenaline surges: A sudden flood of adrenaline, whether from anxiety, a traumatic event, or a near-accident, can cause trembling that feels identical to cold-induced chills.
- Hormonal changes: Menopausal hot flashes and night sweats often alternate with chills as the body overcorrects its temperature regulation. The hypothalamus becomes more sensitive to small temperature fluctuations during hormonal shifts.
- Anesthesia: As many as two in three people experience chills and shivering after general anesthesia. Operating rooms are kept cool, and anesthesia disrupts your body’s normal temperature regulation, so your core temperature often drops during surgery.
- Drug or alcohol withdrawal: The nervous system becomes hyperactive during withdrawal, producing shaking, sweating, and chills as it recalibrates without the substance it adapted to.
- Certain cancers: Some blood cancers like leukemia can cause recurring chills, often alongside night sweats and unexplained weight loss.
When Chills Signal Something Serious
Most chills are harmless and resolve on their own once you warm up, your fever breaks, or the triggering event passes. But certain combinations of symptoms alongside chills deserve prompt attention. A stiff neck paired with fever and chills can indicate meningitis. Confusion or disorientation with a high fever may signal a severe infection. Repeated vomiting or diarrhea with chills can lead to dangerous dehydration. Seizures during a fever, particularly in children, require emergency care.
For infants under three months old, any fever with chills warrants immediate medical evaluation, since their immune systems are still developing and infections can escalate quickly. In adults, chills that persist for days without an obvious cause, or that come with unexplained weight loss or drenching night sweats, are worth investigating with a healthcare provider.