Shivering and chills frequently appear just before or during a fever, as the body raises its temperature to fight infection — you feel cold even though your temperature is rising. This is common with flu, urinary infections, and, in some regions, malaria. The chills usually pass as the fever develops or breaks.
If you feel cold all the time without an infection, other causes include iron-deficiency anemia, an underactive thyroid, low body weight, poor circulation, or low blood sugar. These tend to come on gradually and may be accompanied by fatigue, pale skin, or weight changes, and are worth a doctor's review with simple blood tests.
Seek urgent care if violent shaking chills (rigors) come with a high fever, confusion, a fast heartbeat, or you feel very unwell, as this can signal a serious infection such as sepsis. A clinician can identify the cause. Informational only.