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why do we feel cold when we have a fever

We feel cold at the start of a fever because our brain secretly “turns up” our internal thermostat, so our current body temperature is suddenly too low for the new target, even though it’s actually higher than normal.

Body thermostat reset

  • The hypothalamus in the brain works like a thermostat , normally keeping body temperature around 98.6°F (37°C).
  • When germs or inflammatory chemicals (called pyrogens) appear, they signal the hypothalamus to raise its set‑point to a higher temperature, for example from 37°C to 38–39°C.

Why “cold” when you’re hot?

  • The moment the set‑point jumps up, your actual temperature is suddenly “below target,” so your body reacts exactly as if you were truly cold: you feel chilled, want blankets, and turn up the heat.
  • This mismatch between the higher set‑point and your still‑lower actual temperature is what produces that paradoxical sensation of feeling freezing while the thermometer shows a fever.

Chills, shivers, and goosebumps

  • To reach the new set‑point, the body narrows blood vessels in the skin and gives you goosebumps, reducing heat loss and making your skin feel cool to the touch.
  • Shivering is rapid, tiny muscle contractions that burn energy and generate heat, which is why intense chills often come right before or as the fever climbs.

Why you later feel hot and sweaty

  • Once your body finally reaches the higher set‑point, the chills usually ease and you may just feel warm or flushed, because your temperature now matches the “new normal” your brain ordered.
  • When the infection or inflammation starts to calm down, the set‑point drops back to its usual level, and now your body is “too hot,” so you sweat and throw off blankets as your system works to cool down.

Quick bottom line

  • Feeling cold with a fever does not mean your body is actually too cold; it means your brain has raised the target temperature and is pushing you to help warm yourself up.
  • If you or someone else has a high fever, feels very unwell, is confused, short of breath, or has fever lasting more than a few days, medical evaluation is important, because fever can sometimes signal a more serious condition.

Information gathered from public forums or data available on the internet and portrayed here.