Chills

Chills are the sensation of feeling cold, often with shivering or teeth-chattering, and they are closely linked to fever. When the body is fighting an infection, the brain raises the target temperature; the body then feels cold relative to this new higher set-point and shivers to generate heat — which is why chills so often come just before or as a fever rises. Most chills are part of ordinary infections such as flu, a cold, a chest infection or a urine infection, and settle as the illness is treated or passes. However, the intensity of chills carries information. Mild chills with a low-grade fever are usually part of a run-of-the-mill infection. But violent, uncontrollable shaking chills — called rigors, where the whole body shakes and the teeth chatter — often signal that bacteria or their products have entered the bloodstream, as can happen with a serious kidney or bloodstream infection. Chills with a high fever, confusion, a fast heartbeat, rapid breathing or feeling very unwell can be early signs of sepsis, the body's dangerous over-response to infection. So while most chills are harmless and self-limiting, the combination of shaking chills with a high fever and feeling very unwell should be taken seriously.

• Common infections — flu, colds, chest and throat infections; a frequent cause.
• Urine and kidney infections — a classic cause of chills, sometimes with rigors.
• Any infection with a rising fever — chills often precede the fever.
• Rigors (violent shaking chills) — can signal bacteria in the bloodstream.
• Sepsis — chills with high fever, confusion or feeling very unwell; an emergency.
• Non-infectious causes — occasionally a reaction to medicines, transfusions, or other conditions.
• Simply being cold — chills without fever from a cold environment.

Chills are assessed together with temperature and the search for a source of infection. If an infection needs investigating, blood tests help: a full blood count (the white cell count often rises with infection), inflammatory markers (CRP), and, where a serious bacterial infection or sepsis is suspected, procalcitonin, blood cultures and a lactate. A urine test looks for a urine infection, and other tests (chest X-ray, swabs) target the likely source. Mediora.AI can surface an infection-and-inflammation pattern — a raised white cell count, high CRP or procalcitonin — that supports an active infection, but chills, especially with a high fever or feeling very unwell, are assessed in person, because finding and treating the source promptly is what matters.