Chills are your body’s way of generating heat through rapid, involuntary muscle contractions. Most often, they signal that your body is trying to raise its internal temperature, whether because of an infection, cold exposure, or a shift in your metabolism. But chills can also happen for reasons that have nothing to do with temperature, including strong emotions, low blood sugar, or medication side effects.
How Your Body Produces Chills
A region at the front of your brain called the hypothalamus acts as your body’s thermostat. It constantly monitors your blood temperature and compares it to a set point, much like a thermostat in your house compares the room temperature to whatever you’ve dialed in. When your actual temperature falls below that set point, the hypothalamus sends signals down through your brainstem and spinal cord to activate two responses: your blood vessels near the skin constrict to trap heat inside your body, and your skeletal muscles begin contracting rapidly. Those rapid contractions are the shivering you feel during chills, and they’re surprisingly effective at producing heat.
This system can be triggered in two very different situations. The first is straightforward: you’re in a cold environment and your body temperature genuinely drops. The second is more counterintuitive and far more common when people search “why am I getting chills.” It happens when something raises the set point itself, so your brain perceives your normal body temperature as too low, even though it isn’t.
Chills From Infection and Fever
The most common reason for unexpected chills is that your body is fighting an infection. When your immune system detects bacteria, viruses, or other invaders, it releases signaling molecules that trigger the production of a compound called prostaglandin E2. This compound acts directly on the hypothalamus and raises your temperature set point, sometimes by several degrees.
Here’s why that matters: once the set point jumps to, say, 102°F, your brain treats your current normal temperature of 98.6°F the same way it would treat actual hypothermia. It activates the full heat-generating response: blood vessels constrict (making your skin feel cold and pale), you get goosebumps, and shivering begins. This is why you can feel freezing cold and pile on blankets even though your body is actually heating up. The chills typically stop once your temperature climbs to match the new, higher set point. At that point, you feel hot and flushed instead.
This cycle explains a common pattern during illness. Chills come first as your fever is rising, then you feel burning hot at the peak, and then you sweat as the set point drops back down and your body needs to shed the excess heat. If chills come and go repeatedly over hours, it usually means your fever is spiking in waves.
Rigors: When Chills Become Severe
Not all chills are the same intensity. Regular chills might feel like a mild shiver or a sensation of coldness. Rigors are a more extreme version: uncontrollable, teeth-chattering shaking that can be violent enough to make a bed vibrate. Rigors are your body’s reaction to a severe infection or a large release of bacteria or viruses into the bloodstream. If you experience shaking this intense, especially with a high fever, it warrants prompt medical attention because it can indicate a serious systemic infection.
Chills Without Fever
If you’re getting chills but don’t have a fever, several other explanations are worth considering.
Cold exposure is the simplest. Even mild cold, like sitting in an air-conditioned room in light clothing, can trigger chills if your core temperature dips slightly. This is normal thermoregulation doing exactly what it’s supposed to do.
Low blood sugar (hypoglycemia) can cause chills, shakiness, sweating, and a sense of feeling cold. Your body needs glucose to maintain its temperature, and when levels drop too low, heat production falters. This is more common in people with diabetes who take insulin, but it can happen to anyone who hasn’t eaten in a long time or after intense exercise.
Underactive thyroid (hypothyroidism) is a classic cause of persistent cold sensitivity. Your thyroid hormones directly control how fast your cells burn fuel for energy and heat. When thyroid hormone levels are low, every cell in the body slows its metabolism, and one of the earliest and most noticeable symptoms is feeling cold when others around you are comfortable. In severe, untreated cases, this can progress to intense cold intolerance, extreme fatigue, and even loss of consciousness.
Anemia, a shortage of red blood cells, reduces the amount of oxygen delivered to your tissues. Since oxygen is essential for the metabolic reactions that generate body heat, people with significant anemia often feel cold, especially in their hands and feet, and may experience chills.
Intense emotional or physical stress can also produce chills. During a panic attack or a moment of acute anxiety, your nervous system floods your body with adrenaline. This causes blood vessels near the skin to constrict, redirecting blood to your muscles and organs, and can leave you shivering even when you’re not cold.
Emotional Chills and Frisson
You may have noticed chills running down your spine during a powerful piece of music, a moving speech, or a moment of awe. This sensation, sometimes called frisson, is real and well-documented. It turns out that people who experience it tend to have a higher volume of nerve fibers connecting the part of the brain that processes sound to the areas that process emotion. Those denser connections allow the two regions to communicate more effectively, so an unexpected key change in a song or a soaring vocal moment can trigger a physical response that feels identical to a temperature-related chill.
Not everyone experiences frisson to the same degree. Some people get it frequently from music, films, or even certain textures, while others rarely or never do. It’s harmless and is generally considered a sign of heightened emotional responsiveness rather than any medical concern.
Medications That Can Cause Chills
Certain medications list chills as a side effect, though this is typically uncommon. Some blood pressure medications can cause chills along with changes in skin color in the fingers and toes, because they affect how blood vessels constrict. Medications that influence serotonin levels in the brain can occasionally trigger a cluster of symptoms that includes chills, unusual sweating, muscle twitching, and restlessness. If you notice chills starting shortly after beginning a new medication or changing a dose, it’s worth flagging to whoever prescribed it.
Anesthesia is another well-known trigger. Many people experience shivering during recovery from surgery, partly because operating rooms are kept cool and partly because anesthetic drugs interfere with the body’s temperature regulation. This type of shivering is temporary and resolves as the medication wears off.
Patterns That Signal Something Serious
Isolated chills from a cold, a skipped meal, or a brief illness are rarely dangerous. But certain patterns deserve attention. Chills paired with a fever above 100.4°F (38°C) that lasts more than five days may indicate an infection that your body can’t clear on its own. Chills accompanied by confusion, a stiff neck, trouble breathing, repeated vomiting or diarrhea, a rash, or joint pain and swelling can point to more serious conditions including meningitis or sepsis.
For infants under three months old, any fever with chills warrants immediate medical evaluation. Young babies lack the immune maturity to fight infections effectively, and what looks like a minor illness can escalate quickly.
Chills that keep coming back over weeks without an obvious cause, especially alongside fatigue, unexplained weight changes, or persistent cold sensitivity, may point toward a thyroid disorder, anemia, or another underlying condition that a blood test can usually identify.