Chills are your body’s way of generating heat through rapid muscle contractions, and they can signal anything from a brewing infection to low blood sugar to an emotional response. Most often, chills accompany a rising fever as your body fights off a virus or bacterial infection. But they also show up in situations that have nothing to do with illness, which is why understanding the context matters.
How Your Body Produces Chills
A region at the base of your brain acts as your internal thermostat. When it detects that your body temperature needs to rise, whether because you’re cold or because your immune system is resetting your temperature set point during an infection, it triggers a cascade of responses. First comes blood vessel constriction in your skin, which keeps warm blood closer to your core. Then comes shivering, the involuntary rapid contraction of your muscles that generates heat as a byproduct.
During an infection, immune signals essentially “trick” your thermostat into thinking your normal temperature is too low. Your brain responds by making you feel cold even when you’re not, triggering chills to drive your temperature up. That’s why you can feel freezing under a blanket while running a fever of 102°F.
Infections: The Most Common Cause
The flu, COVID, colds, and other viral infections are the most frequent reason people experience chills. Bacterial infections also commonly cause them, including pneumonia, urinary tract infections, and listeria. When chills accompany a fever (defined as a body temperature of 100.4°F or higher), an infection is the likeliest explanation.
Not all fevers are equal. A low-grade fever runs between 99.1°F and 100.4°F and typically accompanies mild infections your body can handle on its own. Moderate fevers (100.6°F to 102.2°F) and high fevers (102.4°F and above) warrant closer attention, particularly if they persist for more than a few days or come with other concerning symptoms like confusion, difficulty breathing, or severe pain.
When Chills Signal Something More Serious
There’s an important distinction between ordinary chills and what clinicians call rigors. Rigors involve intense, uncontrollable shaking, teeth chattering, and goosebumps across the body. They look almost seizure-like and feel far more violent than a simple shiver. Rigors are frequently an early warning sign of sepsis, a life-threatening reaction to infection where the immune response starts damaging the body’s own tissues.
If you or someone near you experiences violent shaking alongside a high fever, rapid heart rate, or confusion, that combination needs emergency medical attention. Sepsis progresses quickly, and rigors can be one of the first visible clues that a bacterial infection has entered the bloodstream.
Chills Without a Fever
Plenty of conditions cause chills with no fever at all, and these tend to puzzle people the most. Low blood sugar is a common culprit, especially in people with diabetes. When blood glucose drops too low, your body releases stress hormones that can trigger shaking and chills alongside dizziness and sweating.
Hormonal shifts during menopause frequently cause chills as well. Hot flashes and night sweats get more attention, but the rapid temperature fluctuations of menopause can swing in both directions, leaving you shivering after a wave of heat passes. Anemia, where your blood carries fewer oxygen-rich red blood cells, can also make you feel persistently cold and prone to chills because your body struggles to regulate its temperature efficiently.
Other causes of chills without fever include:
- Panic attacks: the surge of adrenaline during intense anxiety can produce visible trembling and a chilled sensation
- Drug or alcohol withdrawal: the nervous system rebounds from the absence of a substance it adapted to
- Hangovers: dehydration and metabolic disruption after heavy drinking
- Psychological trauma: people with PTSD or those who’ve just experienced a frightening event often tremble from the flood of stress hormones
Chills After Surgery
Up to two in three people experience chills and shivering after waking from general anesthesia. The exact mechanism isn’t fully understood, but it’s likely related to your core body temperature dropping during surgery. Operating rooms are kept cool, your body’s thermoregulation is suppressed by anesthesia, and you may be exposed for an extended period. When consciousness returns, your brain detects the temperature gap and kicks shivering into high gear. Postoperative chills are uncomfortable but typically resolve within 20 to 30 minutes as your body warms back up.
Medication-Related Chills
Certain medications, particularly those given by IV infusion, can trigger rigors as a side effect. This is especially common with some cancer treatments and antifungal drugs. The body reacts to the medication itself, producing shaking episodes that range from mild shivers to intense rigors. If you experience chills during or shortly after receiving an infusion, your care team can adjust the rate or add medications to manage the reaction.
Emotional Chills Are Real, Too
Not all chills are medical. That shiver down your spine during a powerful piece of music or an emotional movie scene is a phenomenon called frisson. Brain imaging studies have shown that these “musical chills” trigger a release of dopamine, the same reward chemical involved in eating, sex, and other pleasurable experiences. The response involves ancient reward circuitry in the brain and correlates directly with how pleasurable someone rates the experience. About 50 to 80 percent of people report experiencing frisson at some point, and it’s more common in people who score high on openness to experience.
Chills in Children
Children experience chills for the same reasons adults do, but parents should pay particular attention to how quickly a child’s temperature rises. Most febrile seizures, the brief convulsions that can frighten parents, occur in the first few hours of a fever during the initial temperature spike. Children between 6 months and 5 years old are most susceptible, with peak risk between 12 and 18 months. Chills in a young child with a rapidly climbing fever deserve prompt attention, not because febrile seizures are typically dangerous on their own, but because a fast-rising fever in a small child can signal an infection that needs treatment.
What to Do When You Have Chills
Your instinct when chills hit is to pile on blankets, and that’s fine for comfort in the short term. But if you’re running a fever, bundling up too heavily can trap heat and push your temperature higher. A light blanket, warm fluids, and a comfortable room temperature strike the right balance. Stay hydrated, since fever increases fluid loss through sweat.
If your chills come without a fever, think about context. Did you skip a meal? Are you anxious? Have you recently changed a medication? Chills that show up once and disappear are rarely a concern. Chills that recur over days, come with drenching night sweats, or accompany unexplained weight loss point to something that needs investigation, since persistent patterns like these can occasionally signal conditions as serious as leukemia or chronic infections.