What should you know about rigor fever?

A rigor is a sudden episode of intense shaking, chills or teeth chattering that may happen as body temperature rises. Fever with rigors can accompany infections affecting the airways, skin, urinary system or bloodstream. The fever itself is a symptom, not a diagnosis: common cold, acute bronchitis, COVID-19, cellulitis, chickenpox, croup, bronchiolitis and brucellosis are among conditions that can present with fever in different settings. The pattern, age, other symptoms, travel history and medical conditions guide assessment.

Rest, drink fluids in small regular amounts and use a thermometer if available so you can describe the pattern clearly. Wear light clothing and avoid aggressive cooling while shivering. Paracetamol may help discomfort for some people when used according to the label and personal medical advice; check before giving it to a child or combining products. Arrange medical advice when fever persists, returns after improving, or comes with a focused symptom such as breathing difficulty, painful urination, rash or severe headache.

Get emergency help for trouble breathing, blue lips, collapse, a seizure, severe confusion, a stiff neck, a rapidly spreading rash, or inability to keep fluids down. A baby with a fever, an older person who becomes suddenly confused, or anyone with a weakened immune system needs prompt clinical advice. Severe shaking with a very unwell appearance, rapid breathing or faintness should be assessed urgently because a serious infection needs to be considered.

Tell the clinician when the fever and shaking began, the highest reading you recorded, recent medicines, travel, sick contacts and any rash, cough, pain or urinary symptoms. Ask what examinations or tests are needed, how to maintain fluids, and which changes mean you should return immediately.