Chills are your body’s way of generating heat quickly. When your brain detects that your body temperature is too low, or when something tricks it into thinking the temperature needs to rise, it triggers rapid muscle contractions (shivering) and tightens blood vessels near your skin to conserve warmth. The causes range from completely harmless to worth paying attention to, and the context around your chills is what tells you which category you’re in.
How Your Body Creates Chills
A region deep in your brain acts as an internal thermostat. When it senses that your core temperature has dropped below its target, or when that target gets shifted upward, it activates a chain reaction. Blood vessels near the skin constrict, pulling warm blood toward your organs. Your muscles begin contracting rapidly, sometimes visibly as shivering, sometimes as a subtle internal trembling. This muscular activity generates heat the same way exercise does, just involuntarily.
That cold, shaky feeling you recognize as “the chills” is this system working in real time. Your body is essentially turning itself into a space heater.
Fever and Infection: The Most Common Cause
When you’re fighting an infection, your immune system releases signaling molecules that travel to the brain and push your internal thermostat’s set point higher. Your normal temperature of around 98.6°F suddenly registers as “too cold” to your brain, even though nothing about the outside temperature has changed. The result is vasoconstriction and shivering as your body works to reach the new, higher target. This is why chills often hit before a fever fully develops. You feel freezing, pile on blankets, and then an hour or two later you’re burning up.
Virtually any infection can cause this, from the flu and COVID to urinary tract infections and pneumonia. The chills themselves aren’t dangerous. They’re a sign your immune system has detected a threat and is ramping up the fight.
When Chills Signal Something Serious
There’s a difference between mild chilliness and what clinicians call “rigors,” which are episodes of violent, uncontrollable shaking that persist even under thick blankets. Rigors are more strongly associated with bacterial infections in the bloodstream. If you experience intense shaking chills alongside a high fever, rapid heartbeat, confusion, or extreme fatigue, that combination can point toward a serious systemic infection that needs prompt medical attention.
Chills Without a Fever
Not every episode of chills means you’re getting sick. Several common conditions make your body more prone to feeling cold and shivery.
- Cold exposure. The most obvious cause. If the air around you is cold enough, your body will start shivering to compensate. This is especially common after intense exercise outdoors. Your muscles generated plenty of heat while you were moving, but once you stop, your sweat-dampened body cools rapidly.
- Low blood sugar. When your blood sugar drops, your body releases stress hormones that can trigger shaking and chills. This is common in people with diabetes who take insulin, but it can also happen if you’ve gone too long without eating.
- Anemia. Without enough iron in your blood, your body struggles to deliver oxygen efficiently. Common symptoms include constant fatigue, pale skin, and a persistent feeling of being cold with frequent chills.
- Underactive thyroid. Your thyroid gland controls your metabolism, which is essentially how much heat your body produces at rest. When it underperforms, you become more sensitive to cold and may notice chills in temperatures that don’t bother other people.
Stress, Anxiety, and Panic Attacks
Chills are a recognized symptom of panic attacks, and they catch many people off guard. During a panic attack, your nervous system floods your body with adrenaline as part of the fight-or-flight response. Your heart rate spikes, blood rushes to your major muscles, and blood vessels near your skin constrict. That redistribution of blood flow can leave you feeling suddenly cold, shaky, or both. Some people experience alternating waves of chills and hot flashes within the same episode.
You don’t need a full panic attack for this to happen, either. Intense stress or anxiety can trigger a milder version of the same response, producing goosebumps and a chill that seems to come out of nowhere.
Hormonal Changes During Menopause
Hot flashes get most of the attention during menopause, but chills are part of the same phenomenon. A hot flash begins when your body sweats and opens blood vessels near the skin to dump heat. Your core temperature drops, and once it crosses a lower threshold, shivering kicks in. Many women describe a cycle of feeling suddenly overheated, then abruptly cold and shivery within minutes.
The underlying mechanism involves changes in the brain’s thermostat. As estrogen levels decline, the comfort zone between “too hot” and “too cold” narrows significantly. Small fluctuations in core temperature that your body would normally ignore now trigger full sweating or shivering responses. This is why some women in perimenopause and menopause experience chills even without a preceding hot flash.
Emotional Chills Are a Real Phenomenon
If you’ve ever felt a wave of tingling chills run down your spine while listening to a powerful piece of music, watching an emotional movie scene, or hearing an inspiring speech, that’s not imaginary. Researchers call these “aesthetic chills” or “frisson,” and they have a distinct neurological basis.
These chills are driven by dopamine, the same brain chemical involved in pleasure, reward, and motivation. Brain imaging studies show that the pleasure derived from music is associated with dopamine release in the brain’s reward centers. In one striking experiment, giving participants a dopamine-boosting compound significantly increased the number of chills they experienced while listening to music, while a dopamine-blocking compound reduced them.
The current theory is that aesthetic chills happen when something violates your expectations in a pleasurable way. A surprising key change in a song, an unexpected plot twist, a moment of beauty you didn’t see coming. Your brain’s prediction system registers the surprise, dopamine surges, and you get that physical rush of chills. Not everyone experiences them with the same frequency, and some people rarely get them at all.
Medication Side Effects
Certain medications can trigger chills as a side effect, either directly or by altering how your brain regulates temperature. Some of the more common culprits include chemotherapy drugs, biologic therapies used for autoimmune conditions, and certain antibiotics given intravenously. Opioid withdrawal is another well-known trigger, producing intense chills and shivering as the body readjusts.
Some drug interactions can also cause temperature dysregulation. Combining certain antidepressants with other serotonin-affecting medications, including some pain relievers and even the supplement St. John’s wort, can provoke a reaction that includes chills, tremor, and fever. If chills start shortly after beginning a new medication or combining medications, that timing is worth noting and reporting.
When Cold Exposure Becomes Dangerous
Shivering in cold weather is normal and protective, but it has limits. Mild hypothermia begins when your core temperature drops to 90-95°F, and shivering is usually intense at this stage. As your core temperature continues to fall below about 86-90°F, shivering actually stops, which is a dangerous sign. It means your body has exhausted its ability to generate heat through muscle contraction. If you or someone around you was shivering heavily in the cold and then suddenly stops while still exposed, that’s an emergency rather than an improvement.
Reading Your Chills in Context
A single episode of chills with no other symptoms usually means your body got cold and corrected itself. Chills that come with a fever, sore throat, or body aches point toward an infection your immune system is handling. Chills that recur without obvious cause, especially alongside fatigue, weight changes, or persistent cold sensitivity, may reflect an underlying condition like thyroid dysfunction or anemia that a simple blood test can identify.
The intensity matters too. Brief chills that pass in minutes are rarely concerning. Prolonged, violent shaking that doesn’t respond to warming up, particularly with a high fever, warrants more urgency. And chills that show up only in specific emotional or environmental contexts, like after exercise, during stressful moments, or while listening to music, are typically your nervous system doing exactly what it’s designed to do.