Chills happen when your brain detects that your body temperature is too low, or when it raises its internal “target temperature” in response to an infection or other trigger. The result is rapid, involuntary muscle contractions (shivering) that generate heat. But infections are only one piece of the picture. Chills can stem from dozens of causes, ranging from a cold room to a panic attack to a drop in blood sugar.
How Your Body Produces Chills
A small region in your brain called the hypothalamus acts as your body’s thermostat. It continuously monitors signals from temperature sensors in your skin and core, and when it detects a gap between your actual temperature and its target, it triggers a response. If the gap means you’re too cold, the hypothalamus activates a motor center that causes your skeletal muscles to contract rapidly and rhythmically. That’s the shivering you feel. These contractions burn energy and produce heat, which is why chills often leave you feeling exhausted afterward.
During an infection, the process works a little differently. Your immune system releases chemical signals that effectively turn up the thermostat’s set point. Your normal 98.6°F suddenly registers as “too cold” to your brain, so it fires up the same shivering response to close the gap. That’s why you can feel freezing cold while running a fever.
Infections and Fever
The most common reason people experience chills is an infection, whether viral (like the flu or COVID-19), bacterial (like a urinary tract infection or pneumonia), or fungal. The pattern is familiar: chills come on as the fever climbs, then give way to sweating as the fever breaks and the thermostat resets downward.
Most fevers caused by common infections resolve on their own. However, a fever above 104°F (40°C) warrants a call to your doctor. Seek immediate medical attention if chills and fever come with confusion, a stiff neck, trouble breathing, seizures, loss of consciousness, or severe pain anywhere in the body.
Sepsis: When Chills Signal an Emergency
Sepsis is a life-threatening response to infection in which the immune system begins damaging the body’s own organs. Chills and fever are its most recognizable early symptom. In one study of over 400 sepsis patients, more than 61% presented with fever and chills as their primary complaint.
The World Sepsis Day committee created a mnemonic to help people recognize the condition: slurred speech or confusion, extreme shivering or muscle pain, passing no urine all day, severe breathlessness, a feeling that you might die, and skin that looks mottled or discolored. If chills appear alongside any combination of these symptoms, treat it as a medical emergency.
Cold Exposure and Hypothermia
Prolonged exposure to cold air, wind, or water is an obvious trigger for chills. Your body shivers to generate warmth, and in most cases, getting to a warm environment stops the cycle. But when your core temperature drops below 95°F (35°C), you’ve entered mild hypothermia. Symptoms at this stage include shivering, fatigue, nausea, and pale skin.
Here’s the dangerous part: shivering typically stops once core temperature falls to around 86 to 90°F (30 to 32°C). That cessation isn’t a sign of recovery. It means the body has lost its ability to warm itself. At this point, some people begin removing their own clothing, a phenomenon called paradoxical undressing, driven by confused nerve signals. Anyone who has stopped shivering but is still in a cold environment needs emergency help.
Low Blood Sugar
When blood sugar drops below about 70 mg/dL, the body releases a surge of adrenaline as part of its fight-or-flight response. This triggers a cluster of symptoms: shakiness, a pounding heartbeat, sweating, tingling, and anxiety. The shakiness can feel a lot like chills and is sometimes mistaken for them. People with diabetes who take insulin are most at risk, but skipping meals, intense exercise, or heavy alcohol consumption can cause low blood sugar in anyone.
If you notice chills alongside sudden hunger, lightheadedness, or irritability, eating or drinking something with fast-acting sugar (juice, glucose tablets, regular soda) usually resolves symptoms within 15 minutes.
Hormonal Changes
During perimenopause and menopause, fluctuating hormone levels make the brain’s internal thermostat more sensitive. Most people associate this stage of life with hot flashes, but cold flashes are equally real. The same hormonal instability that causes a sudden wave of heat can swing the other direction, leaving you with chills and goosebumps that come on without warning.
Both caffeine and alcohol can make these episodes worse by further disrupting the body’s temperature regulation systems. Thyroid disorders can also cause chills. An underactive thyroid slows metabolism and reduces heat production, making you feel cold even in comfortable environments. This is one of the most overlooked hormonal causes of persistent chills without fever.
Anxiety and Panic Attacks
Chills are a recognized symptom of panic attacks. The mechanism is essentially the same adrenaline-driven fight-or-flight response that kicks in during a physical threat. Your heart rate spikes, breathing quickens, and blood flow shifts toward your large muscles and away from your skin. That redistribution of blood can leave your extremities feeling cold while the rest of your body feels hyperactivated. The chills often hit alongside sweating, chest tightness, and a sense of dread.
These episodes are frightening, partly because they mimic serious medical conditions. If you experience recurrent chills during moments of intense anxiety but have no fever or other illness, the cause is likely autonomic rather than infectious.
Medications and Medical Treatments
Certain medications trigger chills as a side effect, particularly drugs delivered by infusion. Some cancer treatments cause the immune system to release inflammatory compounds as they destroy targeted cells. In studies of patients receiving rituximab (a common treatment for lymphoma and autoimmune conditions), 13% to 33% developed rigors, which are intense, uncontrollable episodes of shivering. For antithymocyte globulin, a drug used in transplant medicine, that rate climbed to roughly 55%.
Vaccines frequently cause chills as well, particularly in the first 24 to 48 hours. This is a normal sign that your immune system is responding. Antifungal medications and some antibiotics can also trigger shivering during infusion.
Chills After Surgery
Shivering after anesthesia is one of the most common post-surgical complaints. A recent meta-analysis found an overall incidence of 34%, though individual studies report rates as high as 60 to 70% after general anesthesia. Anesthetic drugs widen the range of temperatures your brain considers “normal,” so your body doesn’t fight heat loss during surgery the way it normally would. When the drugs wear off, the thermostat snaps back to its usual setting, detects that your core temperature has drifted down, and triggers shivering to close the gap. Interestingly, post-surgical shivering sometimes occurs even in patients whose temperature stayed normal throughout the procedure, suggesting the anesthesia itself can directly stimulate a shivering-like muscle response.
Other Common Triggers
- Anemia. Low red blood cell counts reduce oxygen delivery to tissues, which can impair heat production and leave you feeling persistently cold.
- Dehydration. Your body relies on adequate fluid volume to regulate temperature. Even moderate dehydration can make you more sensitive to cold.
- Sleep deprivation. Core body temperature drops naturally during sleep. Chronic sleep loss can interfere with normal temperature cycling, sometimes producing chills at odd hours.
- Intense exercise. After strenuous activity, your body can overcorrect as it tries to cool down, leading to post-exercise chills. Wet clothing and wind exposure compound the effect.
- Strong emotions. Fear, awe, or deeply moving experiences can trigger a brief wave of chills and goosebumps. This is an involuntary nervous system response and is completely harmless.
Chills With Fever vs. Chills Without Fever
This distinction matters because it narrows the likely cause. Chills paired with fever almost always point to an infection or inflammatory process. Your immune system is actively fighting something, and the thermostat has been deliberately reset higher.
Chills without fever suggest a different category of triggers: cold exposure, hormonal fluctuations, low blood sugar, anxiety, anemia, or medication side effects. These causes act on the nervous system or blood flow rather than the immune system. Persistent chills without fever that don’t have an obvious explanation (like a cold room) are worth investigating, particularly if they come with fatigue, weight changes, or hair loss, which could point toward a thyroid issue.