Chills are your body’s way of generating heat, usually through rapid, involuntary muscle contractions that you experience as shivering and feeling cold. They happen when your brain decides your body temperature needs to be higher than it currently is, whether because of a fever, cold exposure, or other triggers. Chills are a symptom, not a condition on their own, and understanding what drives them helps you figure out what your body is telling you.
Why Your Body Produces Chills
The process starts in a small region of your brain called the hypothalamus, which acts as your body’s thermostat. Under normal conditions, it keeps your core temperature hovering around 98.6°F (37°C). When something causes that set point to shift upward, like an infection triggering a fever, your brain essentially “thinks” your current normal temperature is too cold. It responds the same way it would if you stepped outside in winter without a coat.
Your hypothalamus activates several warming strategies at once. Blood vessels near the skin’s surface narrow to reduce heat loss, which is why your hands and feet may feel icy. Your body ramps up its metabolic rate by releasing stress hormones like epinephrine and norepinephrine, a process called chemical thermogenesis. And if those measures aren’t enough, the shivering motor center in your hypothalamus kicks in, triggering the rapid muscle contractions you feel as shaking or trembling. All of this works together to push your temperature up to match the new, higher set point.
Once your temperature reaches that new target, the chills stop, even though you now have a fever. This is why chills typically come at the beginning of a fever rather than lasting through the whole illness.
Chills vs. Rigors
Not all chills are created equal. Mild chills might feel like a gentle shiver or goosebumps, while severe episodes, called rigors, involve dramatic, uncontrollable shaking that can last anywhere from minutes to hours. During a rigor, your teeth may chatter and your whole body may tremble visibly, all while your temperature climbs. The fever that accompanies rigors tends to be quite high.
One important distinction: during a rigor, you remain conscious and aware of your surroundings, even if you feel confused from the high temperature. You can still respond to questions or follow simple instructions like “open your eyes.” A seizure, by contrast, also involves jerky movements but the person is unaware of their surroundings and doesn’t respond. This difference matters if you’re watching someone else go through an intense episode of shaking.
Common Causes of Chills
Infections are the most frequent trigger. When bacteria or viruses invade your body, your immune system releases chemical signals that raise the hypothalamus’s set point, producing fever and chills as a defense mechanism. The higher temperature helps your immune cells work more efficiently and makes your body a less hospitable environment for pathogens. Common culprits include the flu, pneumonia, urinary tract infections, and bacterial infections like listeria. Sepsis, a dangerous whole-body response to infection, also commonly causes severe chills.
But infections aren’t the only explanation. Chills without fever can occur from straightforward cold exposure, low blood sugar, extreme physical exhaustion, anemia, or strong emotional reactions like fear or anxiety. Hormonal shifts, particularly during menopause, can also produce episodes of chills. Some medications trigger chills as a side effect, and blood transfusion reactions are a well-known cause in hospital settings.
Chills in Children
Children experience chills much the same way adults do, but parents often worry about febrile seizures, which are convulsions triggered by fever in young children. Research suggests the peak temperature reached during a fever matters more than how fast the temperature rises. So while chills signal a fever is building, it’s the overall height of the fever that correlates most with seizure risk.
Children who have their first febrile seizure at a very young age, who have a family history of febrile seizures, or who seize early in the course of a fever are more likely to experience them again. Febrile seizures, while frightening to witness, are generally brief and don’t cause lasting harm in most cases.
What to Do When You Have Chills
Your instinct when you have chills is to bundle up, and that’s fine in the short term. Light blankets and warm fluids can ease the discomfort while your body works to reach its new temperature set point. Staying hydrated matters because fever increases fluid loss through sweating.
What you want to avoid is working against your body in ways that can backfire. Ice baths or cold compresses during active chills will only make the shivering worse, since your body is already fighting to warm up. Over-the-counter fever reducers like ibuprofen or acetaminophen work by lowering the hypothalamus’s set point back toward normal, which addresses the root cause of the chills rather than just the shivering itself.
Chills that come with a mild cold or flu will typically resolve on their own as the infection runs its course. Chills that are unusually severe, that recur repeatedly, or that accompany symptoms like confusion, difficulty breathing, a stiff neck, or a very high fever point to something more serious. Rigors in particular tend to signal bacterial infections or other conditions that may need targeted treatment rather than just rest and fluids.