Chills happen when your brain decides your body needs to be warmer and commands your muscles to contract rapidly to generate heat. This can be triggered by infection, cold exposure, low blood sugar, anemia, hormonal changes, or even strong emotions. The cause is usually straightforward, but persistent or severe chills sometimes signal something that needs medical attention.
How Your Body Produces Chills
A region at the front of your hypothalamus acts as your body’s thermostat. When it senses that your core temperature is too low, or when inflammation tricks it into thinking the temperature needs to be higher (as with a fever), it sends signals down through the brainstem to your spinal cord. Those signals activate your skeletal muscles in rapid, rhythmic contractions: shivering. This is involuntary. You can’t will it to stop because the command bypasses your conscious motor control entirely.
The system has two modes of heat generation. One is shivering, which burns energy through muscle contractions. The other is non-shivering thermogenesis, where specialized fat tissue and cellular processes generate heat without any visible movement. Both are coordinated by the same brain circuitry, and both can contribute to that cold, shaky feeling.
Infection and Fever
The most common reason for sudden chills is your immune system fighting off an infection. When bacteria or viruses invade, your immune cells release signaling molecules that act on the hypothalamus and effectively raise its temperature set point. Your brain now “thinks” your normal 98.6°F is too cold, so it triggers shivering to close the gap. This is why you can feel freezing and pile on blankets even though your body temperature is actually climbing.
Chills that come with a fever are usually caused by viral infections like the flu or COVID, urinary tract infections, pneumonia, or other bacterial infections. The chills typically arrive at the onset of the fever and subside once your temperature stabilizes at the new, higher set point. A single episode of rigors (intense, teeth-chattering shivering) followed by a high fever is a classic pattern that suggests your body is mounting a strong immune response.
Iron Deficiency and Anemia
If you feel cold and shivery on a regular basis, low iron levels could be the reason. Iron-deficiency anemia reduces the amount of oxygen your red blood cells can carry from your lungs to the rest of your body. That oxygen shortage directly impairs two key warming mechanisms: your body’s ability to constrict blood vessels near the skin (which normally keeps heat from escaping) and its ability to ramp up your metabolic rate to produce more heat.
The result is a person who feels cold when others in the same room are comfortable. Research from the National Academies of Sciences confirms that iron-deficient individuals fail to thermoregulate adequately because the reduced oxygen supply undermines the very processes the body relies on to stay warm. If your chills are chronic and you also experience fatigue, pale skin, or brittle nails, a simple blood test can check your iron and hemoglobin levels.
Thyroid Problems
Your thyroid gland sets the pace of your metabolism, and when it underperforms, your internal furnace runs low. People with hypothyroidism have deficient energy metabolism and impaired thermogenesis, which shows up as weight gain, fatigue, and persistent cold intolerance. Even patients who are being treated with thyroid medication can still run cooler than normal. A 2024 study in the Journal of the Endocrine Society found that people with controlled hypothyroidism had significantly lower hand temperatures than healthy controls (about 32°C versus 33°C), suggesting that standard treatment doesn’t fully restore normal heat regulation.
In a comfortable room (roughly 73 to 91°F), your baseline metabolism should generate enough heat to keep you warm without any shivering. When thyroid hormone levels are too low, that baseline heat production drops, and your body has to recruit shivering and other backup systems just to maintain a normal temperature in environments that shouldn’t require them.
Low Blood Sugar
A sudden drop in blood glucose triggers a stress response. Your body floods itself with adrenaline and noradrenaline to push sugar levels back up, and those same hormones cause trembling, sweating, a racing heart, and anxiety. The shaking from low blood sugar isn’t true shivering in the thermoregulatory sense, but it feels very similar and is often described as “chills.” It typically comes on quickly, especially if you’ve skipped a meal, exercised intensely without eating, or have diabetes and taken too much insulin. Eating something with fast-acting carbohydrates usually resolves it within 10 to 15 minutes.
Emotional and Musical Chills
Not all chills mean something is wrong. You’ve probably felt a wave of goosebumps while listening to a powerful piece of music, watching a moving scene in a film, or experiencing a moment of awe. Neuroscientists call this “frisson,” and research at McGill University confirmed that it involves a real release of dopamine, the same brain chemical associated with rewards like food and sex. The response uses ancient reward circuitry in the brain, with one circuit tied to anticipation and prediction and another tied to the emotional limbic system. These chills are a sign of a strong emotional response, not a medical problem.
Medications That Cause Chills
Certain medications can trigger chills even without a fever. Blood pressure medications, some antibiotics, and chemotherapy drugs are the most common culprits. The mechanism varies by drug class. Some affect circulation or metabolic rate, while others provoke an immune-like response. If your chills started around the same time as a new prescription, that timing is worth mentioning to your prescriber. Chills from chemotherapy are particularly common and are often managed with supportive care during infusion sessions.
When Chills Are a Warning Sign
Most chills resolve on their own or point to something manageable. But chills combined with certain other symptoms can indicate sepsis, a life-threatening response to infection that requires emergency treatment. In adults and older children, the red flags to watch for alongside chills include:
- Confusion or slurred speech
- Skin that looks blue, grey, pale, or blotchy (on darker skin, check the palms and soles of the feet)
- Difficulty breathing or breathing very fast
- A rash that doesn’t fade when you press a glass against it
In babies and young children, additional warning signs include a weak or high-pitched cry, unusual sleepiness, and disinterest in feeding. Any of these symptoms alongside chills or a very high or very low temperature warrants calling emergency services immediately.
Chills that keep coming back over days or weeks without an obvious cause, or chills accompanied by unexplained weight loss or drenching night sweats, can sometimes point to chronic infections, autoimmune conditions, or blood cancers like lymphoma. These patterns deserve investigation even if each individual episode seems mild.
Managing Chills at Home
If your chills are part of a mild illness like a cold or flu, the goal is comfort rather than aggressively lowering your temperature. Current medical guidelines actually suggest against routinely using fever reducers just to bring the number down, since fever is part of your immune defense. If the discomfort is significant, over-the-counter fever reducers are a reasonable choice for relief, and they’re preferred over physical cooling methods like cold compresses, which can sometimes make shivering worse by triggering your body to generate even more heat.
Warm blankets, warm fluids, and rest address the immediate discomfort. If your chills aren’t from an infection, the more useful long-term step is identifying the underlying cause. Persistent cold sensitivity that others don’t share often points to thyroid function, iron levels, or circulation as the place to start looking.