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Why do we shiver? From trembling knees to the chills

25.8.2023

Translation: Elicia Payne

Hypothermia, fever, anxiety: your body reacts to these by shivering. In this article you’ll find out why this happens and how it is even essential for survival.

Let’s start with the most logical: when you freeze, your body starts to shiver. Why? The rapid muscle contractions are a protective mechanism to maintain body temperature. To generate heat and thereby increase core temperature, the body uses alternating muscle tension and relaxation. The released heat energy then protects you from hypothermia. At the same time, the blood vessels in the skin contract to minimise heat loss and direct more blood to the centre of the body. If in doubt, the centre must remain warm to protect the internal organs from damage.

Shivering from cold until the teeth chatter

When the whole body is shaken, the muscles of mastication are also involved. They also begin to contract in rapid succession. As a result, the teeth start to chatter – virtually a side effect of shivering. But the chattering demands a lot from the body: the muscle contractions require quite some strength, resulting in the energy requirement of the body increasing by four to five times.

There are theories that shivering protects us from hypothermia in yet another way. If the body temperature drops below a critical level during sleep, you will be jolted awake as the body begins to shiver. This gives you the option to tuck in better or find a warmer place to sleep.

After fever comes chills: why?

So your body uses shivering to generate more heat. If this is the case, isn’t it completely illogical that we sometimes start shivering even when we have a fever? Why does the body generate even more heat through shivering when we are already positively glowing with a fever? Um nochmal eins drauf zu legen, wenn es wirklich ernst ist. The aim of fever is to kill the source of infection (usually bacteria or viruses) with heat. The body heats up as best it can to destroy possible invaders. And that’s where the shivering comes in, in the form of chills. It further raises the body temperature.

Even if the chills really don’t feel good and are also quite consistently demanding on your body, it’s not a dangerous condition per se. It’s a signal from your body that it’s trying to defend itself against infection. And that’s supposed to tell you to respond to the underlying infection. However, as with fever, your body is aiming at something with the shivering and there’s no need to counteract this immediately. It’s only time to act when the body temperature reaches a critical range for too long, i.e. your body has overshot the target. Cooling compresses or fever-reducing medication can help.

Chills may also occur after surgery. This is often due to a combination of factors such as anaesthesia, exposure to cold in the operating room, and the physical stress of the procedure.

Ready to flee: shivering with fear

So we shiver primarily to generate heat, whether to prevent us from freezing (to death) or to fight infection from heat. But why do our knees tremble when we’re anxious? With an «emotional shiver», a different mechanism is at work. An anxiety shiver is a physical reaction to emotional stressors such as excitement or nervousness. This type of shivering is primarily due to the nervous system and the release of stress hormones. The body activates the «fight-or-flight» response. In evolutionary terms, if we are in danger, we must flee or fight. Among other things, the nervous system releases adrenaline to boost the physical response. So that the muscles don’t suffer any damage and we can react quickly, the body warms up as a precautionary measure by starting to shiver.

Incidentally, shivering as a result of anxiety differs from neurological disorders such as Parkinson’s disease or essential tremor. With these disorders, the tremor occurs chronically and without a clear trigger. Anxiety shivers are usually temporary and due to a stressful situation.

Plus, there are techniques to combat anxiety shivers. Deep breathing, meditation, progressive muscle relaxation and mindfulness exercises can help reduce the body’s stress response and control the shivers.

Header image: Patcharanan/Shutterstock

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Anna Sandner

Senior Editor

Anna.Sandner@galaxus.de

Science editor and biologist. I love animals and am fascinated by plants, their abilities and everything you can do with them. That's why my favourite place is always the outdoors - somewhere in nature, preferably in my wild garden.

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Why do we shiver? From trembling knees to the chills

Shivering from cold until the teeth chatter

After fever comes chills: why?

Ready to flee: shivering with fear

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Iron-rich diet: why you don't need to eat spinach for this

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