Feeling cold while your body temperature is rising seems contradictory.
It is not.
The explanation begins with the brain’s temperature-control system.
The brain has a temperature set point
A region of the brain called the hypothalamus helps regulate body temperature.
During some infections, immune signals can cause the hypothalamus to raise the target temperature.
Imagine the body was comfortable near its usual level.
Then the thermostat gets turned higher.
Your current temperature suddenly feels too low
Once the set point rises, the body acts as though it needs to warm up.
Blood vessels near the skin can narrow.
You may shiver.
You want blankets.
You may feel intensely cold even while your measured temperature is climbing.
The sensation matches the new target, not the old one.
Why does shivering help?
Shivering consists of rapid involuntary muscle contractions.
Muscle activity generates heat.
That helps raise body temperature toward the new set point.
The chills are therefore part of the warming response.
Why do you sweat when a fever breaks?
Later, the temperature set point can drop back toward normal.
Now the body may suddenly be hotter than the new target.
Blood flow to the skin increases.
Sweating begins.
The body switches from heat-making mode to heat-losing mode.
Is every fever caused by infection?
No.
Infections are common causes, but inflammation, medications, and other conditions can also raise body temperature.
A fever is a symptom, not a diagnosis.
Are fever chills the same as being cold outside?
The sensation can feel similar, but the trigger is different.
Cold weather lowers heat coming into the body or increases heat loss.
Fever chills are caused by the body’s own temperature target changing.
So fever chills are not a contradiction.
You feel cold because the thermostat moved.
The same body systems connect with Why do we shiver when we are cold?, another everyday effect with its own underlying mechanism.
And that’s the short explanation.
Related explanations: Why do we shiver when we are cold?, Why do we sweat?, and Why do we get thirsty?