Chills are involuntary contractions of muscles whose primary function is to warm the body in the event of hypothermia (= drop in body temperature).

The muscles, in this fight against the cold, contract very quickly (about 10 contractions per second). During the chills, the energy muscular is mainly released as heat (not “mechanical” work), which helps warm the body.

The chills are preceded by an increase in muscle tone which increases heat production. It is usually the masseter (= muscle located in the cheeks) that contracts first, followed by other muscles.

If the chills are an effective reflex to fight against the cold, they can also occur in certain pathological or unusual situations.

We distinguish in particular:

• chills associated with fever
• post-operative chills
• chills occurring in severe burns
• the chills linked to emotions

Chills associated with fever

When the internal temperature rises, in case of fever, it is common to start to shiver and feel cold. This apparently aberrant reaction is due to the fact that the substances responsible for the fever cause disruption of heat-sensitive neurons. Instead of triggering the mechanisms that facilitate heat loss, they help activate the mechanisms to fight the cold, including chills.

Post-operative chills

Many people (up to two-thirds of patients) experience chills after anesthesia. The cause of these chills is not well known but they can occur due to a drop in body temperature, classic after surgery, due to fever, which is also common, but also because of pain. postoperative or the effect of certain anesthetics.

These chills cause discomfort and can also have certain harmful consequences (see below).

The thrill of severe burns

The skin plays a very important role in regulating body temperature (thermoregulation). When large areas of skin are injured, which is the case in severe burns, thermoregulation is affected.

Severe burns are therefore often cold (there are also disorders of the hypothalamus, in the brain, due to the inflammatory reaction which can aggravate this sensation). They may shiver as a result, and therefore should be cared for in a warm room.

Conversely, abnormal sweating, linked to lesions of the sweat glands, can also occur.

The chills linked to emotions

Fear, pleasure, excitement can lead to chills, or rather the feeling of “goose bumps”. Strictly speaking, these are not chills linked to a repetition of involuntary muscle contractions.

The chills are useful in the fight against the cold. However, they cause a high consumption of energy by the muscles, and therefore cannot be maintained for very long. After about an hour, the body gets tired and the ability to shiver decreases.

In case of post-operative chills, several deleterious effects can alter the patient’s condition, if the chill persists. In fact, the patient’s oxygen consumption and cardiac output can increase, as well as the production of certain metabolites (carbon monoxide, lactic acid).

If the chills are related to the drop in body temperature, it is urgent to warm up as soon as possible, if possible.

Sometimes a person feels cold almost constantly, often due to an imbalance in thyroid hormones. If this is the case, a doctor should be consulted for a blood test and to ensure hormonal balance.

In the event of postoperative chills, the medical team may administer certain medications to improve comfort. This is also the case when chills occur in severe burns or in cases of high fever.