Chills when you’re sick are your body’s way of raising its internal temperature. When an infection triggers a fever, your immune system sends chemical signals that tell your brain to reset your body’s thermostat higher. Your body responds by shivering and feeling cold — even though the room is warm — because it is trying to generate heat and reach that new target temperature. Chills are not a sign that something is wrong with your temperature control. They are a sign that it is working.
That explanation covers the most common cause. But chills can also come from other things, and knowing the difference matters. Here is what is actually happening, and when chills deserve more attention.
Why Do I Get Chills When Sick Your Bodys Response?
Your body runs on a set core temperature of about 98.6°F (37°C). That number is not fixed. It is a target, and your brain adjusts it when needed.
The adjustment happens in a region called the hypothalamus, which acts as your body’s thermostat. When immune cells detect an invading pathogen, they release signaling molecules called pyrogens. These chemicals travel to the hypothalamus and cause it to raise the set point — the temperature your body is now trying to maintain.
Here is the key point: your body doesn’t instantly warm up to that new target. It has to get there. And the fastest way to generate heat is through muscle activity. Shivering is rapid, involuntary muscle contraction that produces heat as a byproduct. That shivering is what you experience as chills.
You feel cold during this process for a simple reason. Your actual body temperature is below the new set point. Your skin sensors report that gap to your brain, and you perceive it as cold. You may pile on blankets or feel like you can’t get warm, even in a heated room. Once your body reaches the higher temperature, the chills typically stop.
What Causes Chills Besides Fever?
Fever-related chills are the most common type, but they are not the only cause. Several other mechanisms can produce the same shaking, shivering sensation.
Feeling cold from the environment. Ordinary cold exposure triggers shivering through the same muscle-contraction mechanism. The difference is that your set point hasn’t changed — your body is simply trying to maintain its normal temperature against external cold.
Low blood sugar. When blood glucose drops, the body releases adrenaline and other stress hormones. These can cause shakiness and a cold, clammy feeling that some people describe as chills. This is different from the shivering of fever, but it can feel similar.
Anxiety and panic. The fight-or-flight response releases adrenaline, which can cause trembling, a sense of cold, and goosebumps. These episodes are usually brief and tied to a specific trigger.
Certain medications and medical conditions. Some drugs can cause chills as a side effect. So can hormonal changes, including those around menopause. In rare cases, chills can signal a serious problem such as a blood infection or a reaction to a transfusion.
The pattern matters. Chills that come with a fever and other infection symptoms usually point to a normal immune response. Chills that appear without fever, or that come with confusion, a stiff neck, or trouble breathing, need medical attention.
Why Do Chills Happen Before a Fever Rises?
Chills often arrive before you feel hot, and that sequence confuses people. The reason is that chills are part of how the fever develops, not a separate event.
When the hypothalamus raises its set point, your body is temporarily cooler than it “should” be. During that gap, you shiver and feel cold. This is sometimes called the chill phase of a fever. It lasts until your body temperature catches up to the new target.
Once the temperature reaches the new set point, the chill phase ends. You may then feel hot and flushed. If the fever breaks later, you may sweat as your body releases excess heat to return to normal.
This is why a person can shake under blankets at the start of an illness and then throw the covers off a few hours later. Both are normal stages of the same process.
Are Chills a Sign of a Serious Infection?
Chills are a normal part of many infections, including colds, flu, and other common viral illnesses. They do not by themselves mean the infection is severe.
However, some patterns do warrant prompt medical care. Seek medical attention if chills occur with any of the following:
- A fever that is high or that does not come down with standard fever-reducing medication
- Confusion, unusual sleepiness, or difficulty waking
- A stiff neck, severe headache, or sensitivity to light
- Difficulty breathing or chest pain
- Rapid heart rate that does not settle
- Chills with no fever at all, especially if they are severe or recurring
- Chills in an infant, or in someone with a weakened immune system
These signs can point to a more serious infection or another condition that needs evaluation. They are not proof of a specific illness, but they are reasons to get checked rather than wait.
One point that often gets missed: the intensity of chills does not reliably track how sick someone is. A mild illness can produce dramatic shaking, and a serious one can produce none. How you feel overall — alertness, breathing, hydration, and whether symptoms are worsening — matters more than how hard you shiver.
What Helps Chills Feel Better?
The goal during fever-related chills is comfort, not forcing the temperature down. The chills will stop on their own once your body reaches its new set point.
Light layers and a blanket can ease the cold feeling during the chill phase. Once you feel hot and flushed, remove extra layers so your body can release heat. Drinking fluids helps replace what you lose through sweating and breathing, and it supports normal body function during illness.
Over-the-counter fever reducers can lower temperature and ease discomfort. They do not treat the underlying infection, and they are not needed for every fever. Follow the label directions, and check with a pharmacist or clinician if you take other medications or have liver or kidney conditions.
Rest matters. Your immune system is doing real work, and shivering itself uses energy. Sleep and fluids support recovery more than any single remedy.
Do not use ice baths or cold water to bring down a fever. These can cause shivering that raises body temperature further and can be dangerous. This is one area where common practice and safe practice diverge.
When Should Chills Worry You?
Most chills with fever resolve as the illness runs its course. The timeline varies by infection, and there is no single number that applies to everyone.
Pay attention to direction rather than speed. Symptoms that steadily improve are reassuring. Symptoms that worsen after a few days, or that return after improving, deserve a call to a clinician.
Get urgent help for chills with confusion, a stiff neck, trouble breathing, or a fever in a very young infant. These are situations where waiting is not safe.
For most adults, chills are an uncomfortable but ordinary part of being sick. They are evidence that your body’s temperature regulation is responding the way it is designed to.
Frequently Asked Questions
Why do I get chills when I have a fever?
Chills happen because your brain raises its temperature set point during infection, leaving your body temporarily cooler than its new target. Shivering generates heat to close that gap.
Do chills mean my fever is getting worse?
Not necessarily. Chills usually signal that your temperature is rising toward a new set point, which is a normal part of the fever response. How severe the illness is depends on other symptoms, not on how hard you shiver.
Can you have chills without a fever?
Yes. Cold exposure, low blood sugar, anxiety, some medications, and certain medical conditions can all cause chills without a fever. Chills with no fever that are severe or keep returning should be checked by a clinician.
Should I bundle up or cool down when I have chills?
Use light layers during the chill phase, then remove extra blankets once you feel hot and flushed. Avoid ice baths or cold water, which can trigger more shivering and raise body temperature further.
