Mon Feb 12

why do we shiver when we feel cold?

Written by: Charlotte Phelps, Senior Teaching Fellow, Medical Program, Bond University

“Why do we shiver when we feel cold?” – Syeda, age 10, from Karachi

What a cool question, Syeda!

Our bodies like to be nice and warm, usually around 37°C ^[1]. This allows our internal functions to work at their best. But our bodies are constantly losing heat to the outside air.

When it’s cold outside, or if we jump into a cold swimming pool, or even if the air-conditioning is a bit strong, our body temperature can lower, sometimes to levels that are uncomfortable.

If our body temperature drops too low, our heart, nervous system and other organs are not able to work normally ^[2]. If it falls to extremely low temperatures, called hypothermia, this can cause some organs to completely fail ^[3].

Luckily, our bodies have their own internal heaters to protect us against small changes in temperature. This is mostly thanks to the actions of our muscles, through a process called thermoregulation ^[5]. It’s this process that leads our bodies to shiver when we’re chilly.

Muscles are our bodies’ personal heaters

When our muscles twitch, they generate movement ^[6]. This is called “muscle contraction”, and can involve the muscles tightening and shortening.

Muscle contractions help us walk around, smile, lift heavy objects and high-five each other.

Moving our muscles also generates a bit of heat ^[7]. With many muscles moving ^[8] most of the time, this helps our bodies stay nice and warm.

We’ll often hunch our necks, tense up, and rub our shoulders when cold. Shivering usually follows to help warm us up. Christian Moro

The more our muscles move, the more heat they generate. This is why you might feel hot and bothered after running around or playing sports.

On the other hand, when we stop moving our muscles, we start to cool down. This is one of the reasons we cover up with bedsheets at night.

What about the shiver?

Shivering ^[10] is the rapid contractions of our muscles over and over. This doesn’t generate any significant movement, but instead releases heat that helps to warm us up.

Most of the time we don’t have control over when our brain tells our muscles to shiver. We have special sensors throughout our body ^[11] that pick up when our system is cold, and our brain then responds by telling the muscles to start shivering.

And we aren’t the only ones who shiver! All mammals ^[12] have the ability to shiver, so your pet cat or dog might shiver when they’re cold too. Even birds ^[13] shiver.

When it’s a chilly day outside, you might also notice you get goosebumps ^[15]. Goosebumps happen when tiny muscles connected to the hair follicles (from which our hair grows) tighten. This causes the little hairs on our arms to stand up, helping to trap in warm air and slow down body heat loss to the outside.