Yes, chills typically come before a fever. They are your body’s mechanism for generating heat, and they occur during the window between when your brain raises its internal temperature target and when your actual body temperature catches up. That gap, which can last anywhere from minutes to an hour or more, is when you feel cold, shaky, and miserable even though your temperature is actively climbing.
Why Your Body Shivers Before the Fever Hits
When your immune system detects an infection, it releases signaling molecules (including one called IL-1 and another called TNF) that travel to a temperature control center deep in your brain. These signals trigger the production of a chemical called prostaglandin E2, which effectively turns up your body’s internal thermostat. Instead of targeting the usual 98.6°F, your brain now wants your core temperature at, say, 101°F or 102°F.
The problem is that your actual body temperature is still normal. To your brain, the gap between where you are and where it wants you to be feels exactly like being out in the cold. So it activates the same defenses it would use on a freezing day: blood vessels near your skin tighten to trap heat inside your core, and your muscles begin contracting involuntarily. That’s the shivering. Those rapid muscle contractions can boost heat production to roughly five times your resting metabolic rate, generating enough warmth to push your temperature up to the new target. Once your core temperature reaches the new set point, the shivering stops and the fever plateaus.
The Three Phases of a Fever
A fever moves through a predictable sequence, and understanding it explains why chills, heat, and sweating each happen at different times.
Phase 1: The chill phase. Your thermostat has been reset upward, but your temperature hasn’t risen yet. You feel cold, your skin looks pale from blood vessel constriction, and you shiver. You may want to curl up under blankets. This is the phase most people are searching about.
Phase 2: The plateau. Your body temperature has reached the new set point. The shivering stops. You now feel hot, your skin is flushed and warm to the touch, and your heart rate is elevated. This is when a thermometer will show a reading at or above 100.4°F (38°C), the threshold most clinicians use to define a fever.
Phase 3: The flush (or defervescence) phase. Your immune system is gaining control, or you’ve taken a fever reducer, and the thermostat resets back to normal. Now your actual temperature is higher than the target, so your body tries to dump heat. Blood vessels dilate, your skin reddens, and you sweat. This is often when people soak through their sheets overnight.
Chills vs. Rigors
Not all chills are created equal. Mild chills feel like a general sense of cold with light shivering, the kind you might get with a common cold or mild virus. Rigors are a more intense version: violent, whole-body shaking that you can’t control, sometimes lasting several minutes. Rigors tend to accompany higher fevers and can signal a more serious infection. The shivering during rigors concentrates in the trunk and thigh muscles, which are the body’s most efficient heat generators.
If you or someone you’re caring for experiences rigors with a fever above 103°F, especially alongside confusion, rapid breathing, a fast heart rate, or very low blood pressure, those are warning signs of a severe infection that needs immediate medical attention.
What to Do During the Chill Phase
The instinct to pile on blankets when you’re shivering is natural, and it’s fine to do so for comfort. Layering clothes, drinking warm fluids, and getting to a warm environment will help ease the discomfort of chills. You’re not “trapping” the fever or making it dangerously worse by staying warm during this phase. Your body is heading toward a set point it’s going to reach regardless.
Once the fever is established and you feel hot rather than cold, switching to lighter clothing and staying hydrated becomes more helpful. A cool, damp cloth on the forehead can provide relief during the plateau phase, though it won’t significantly lower your core temperature on its own.
Timing Fever-Reducing Medication
One common question is whether to take a fever reducer at the first sign of chills or wait until the fever peaks. There’s no single right answer, but there is one practical tip worth knowing: if you do take a fever reducer, keep it on a consistent schedule (every few hours as directed on the label) rather than waiting for symptoms to flare. Taking it only when you feel bad and then letting it wear off creates a rollercoaster effect. Your thermostat drops when the medication kicks in, causing sweating, then rises again as it wears off, bringing back chills. Staying ahead of that cycle is more comfortable than chasing it.
Chills and Fever in Children
Children follow the same chill-then-fever sequence as adults, but the rapid temperature rise that occurs during the chill phase carries an additional concern. Febrile seizures, which are convulsions triggered by fever, are more likely when temperature climbs quickly rather than when it’s already high and stable. Research shows that seizures occurring within the first hour of fever onset carry a significantly higher recurrence risk, roughly four to five times greater than seizures that happen later. For every degree above 101°F, the likelihood of a febrile seizure increases by about 1.8 times.
Febrile seizures are frightening to witness but are usually brief and don’t cause lasting harm. Still, if your child is shivering and then develops a sudden high fever, keeping them comfortable and monitoring for unusual movements or unresponsiveness is important during that initial rapid rise.
Why the Chill Phase Matters
The chill phase is more than just an uncomfortable prelude to fever. It’s an active, energy-intensive process your body uses to fight infection. The higher temperature makes it harder for many bacteria and viruses to reproduce, and it enhances certain immune functions. So when you’re lying under a blanket shaking, your body is doing exactly what it’s designed to do: heating itself up as a defense strategy. The chills are the engine, and the fever is the destination.