What Really Makes You Shiver

Shivering is an involuntary muscle movement where your muscles rapidly contract and relax. Shivering when you're cold is only one cause — there are a few more. According to Healthline, some causes of shivering are a cold environment, after anesthesia, low blood sugar, infection, and fear.

You are probably familiar with shivering when you're cold, and you'll often get goosebumps too. When you are visibly shivering, your body is trying to generate heat. Shivering can boost your surface heat production by 500%, but this will only work for a few hours. Once you run out of glucose, your muscles will get too tired to continue shivering (via Princeton University). If you're cold a lot, you could have an under-active thyroid. See your doctor if you seem to be cold often.

When you've been given anesthesia for a surgery, you might shiver when it starts to wear off. While no one knows why this happens, there are a couple of theories. It could be because your body has cooled down significantly from lying still on an operating table and because anesthesia can interfere with your body's natural ability to regulate its temperature.

Low blood sugar is another cause of shivering, which can happen if you haven't eaten in a bit or your body has trouble regulating blood sugar, such as with diabetes. Other symptoms of low blood sugar include shaking, sweating, heart palpitations, and feeling lightheaded.

Shivering could also be a sign that you are sick, and your body is either fighting off a virus or a bacterial infection. Just like when you're cold, your body is warming up through shivering to try to kill the virus or bacterial infection, which is why you might shiver while you have a fever.

Fear or anxiety can cause shivering due to a spike in adrenaline, a hormone that's connected to your fight or flight response. You may also experience shaking when you're afraid.

Shivering could be due to sepsis, your body's response to an infection, usually a urinary tract infection, or infections in the gut, lung, or skin. Sepsis requires immediate treatment with antibiotics. According to Medical News Today, other symptoms include shortness of breath, increased heart rate, pain, sweating, and confusion. 

Babies do not shiver when they're cold. Instead, they use thermogenesis to stay warm, similar to how hibernating animals stay warm during cold weather. If your baby shivers, it could be due to low blood sugar, which means it's time for a feeding.