Despite wearing multiple layers of clothing, along with a warm hat, gloves, and a scarf, we can still feel cold on the chilliest and windiest days. But what is the problem: are we simply not dressed warmly enough, or could these involuntary muscle contractions be a sign of something more serious? Experts addressed these questions from a scientific perspective, writes Popular Science.

According to Dr. Natasha Bhuyan, a family physician from Phoenix, shivering is the way the human body generates heat when we are cold. It occurs through muscle contractions: shivering can significantly accelerate metabolism, which may lead to faster fatigue. In simple terms, it is indeed an effective way to raise or maintain body temperature, but it requires a large amount of energy.

Like sneezing or getting “goosebumps,” shivering is an involuntary phenomenon. As Dr. Romina Cifuentes explains, shivering is actually a protective response designed to maintain a comfortable body temperature, reports Focus. The hypothalamus is able to detect even slight drops in core body temperature and therefore triggers rapid muscle activity to help preserve thermal stability.

Thus, shivering is a healthy and completely natural response to cold. Moreover, it acts as a kind of built-in thermostat intended to protect us from life-threatening hypothermia.

According to Cifuentes, most people begin to shiver when their body temperature falls below normal. It is worth noting that normal body temperature can vary from person to person, averaging between 36.1 and 37.2 degrees Celsius.

Experts point out that normal body temperature depends on a number of factors, including age, body fat levels, medical conditions, and the body’s ability to adapt to cold.

Most people shiver when they feel cold, but this is not the only possible cause. The “fight-or-flight” response can also make us shiver, as can feelings of anxiety or awe.

However, experts note that illness can also be a cause of shivering. For example, shivering associated with fever means the body is trying to raise its temperature set point—essentially its internal thermostat—in order to fight infection.