Persistent shivering is your body’s most powerful automatic heating mechanism, and it can produce up to five times your normal resting heat output. When you can’t stop shivering, something is either dropping your body temperature or tricking your brain into thinking it has dropped. The cause ranges from simple cold exposure to fever, low blood sugar, anxiety, thyroid problems, or even a medication reaction.
How Shivering Actually Works
Shivering starts with your skin, not your core. Cold receptors in your skin send signals to a temperature-control center deep in your brain, which acts like a thermostat. When that thermostat decides you’re too cold, it triggers rapid, involuntary muscle contractions throughout your body. These tiny contractions burn energy and generate heat fast. You can’t consciously stop them any more than you can consciously stop your heart from beating, because the same automatic nervous system controls both.
This is why shivering feels so exhausting. Your muscles are working hard, even though you’re not moving. At peak intensity, shivering burns calories at roughly five times the rate your body uses while lying still. It’s effective at warming you up, but it drains your energy reserves quickly.
Fever: The Most Common Non-Cold Cause
If you’re shivering but you’re not in a cold environment, a fever is the most likely explanation. When your immune system detects an infection, your white blood cells release signaling molecules that travel through the blood to your brain’s thermostat and raise its set point. Your thermostat might reset from 98.6°F to, say, 102°F. At that moment, your actual body temperature is still normal, but your brain now registers it as too low. So it does exactly what it would do if you walked into a freezer: it makes you shiver.
This is why chills and shivering often come before a fever spikes, not after. You feel freezing cold, pile on blankets, and shiver uncontrollably, all while your temperature climbs. Once your body temperature catches up to the new set point, the shivering stops and you feel hot instead. The whole process is driven by the same chemical pathway that causes inflammation, which is why fever-reducing medications that block that pathway also stop the chills.
Cold Exposure and Early Hypothermia
If you’ve been in cold water, outdoors in winter, or even sitting in aggressive air conditioning for a long time, your shivering is a straightforward cold response. It’s worth knowing the thresholds. Shivering with otherwise normal thinking and coordination happens when core temperature dips to roughly 95 to 98.6°F. That range is considered cold stress, not true hypothermia, and warming up will resolve it.
Mild hypothermia sets in between 90 and 95°F core temperature. At this stage you’re still shivering, but your thinking gets foggy and coordination drops. The dangerous shift happens below about 90°F: shivering may actually stop, not because you’ve warmed up, but because your body has exhausted its ability to generate heat. If someone who was shivering suddenly stops and seems confused or drowsy, that’s a medical emergency.
For rewarming, the most effective approach is applying heat to your chest, armpits, and back, in that order. These areas transfer warmth to your core fastest. Warm blankets, hot water bottles, or heating pads all work. Combine the heat source with insulation (a blanket or sleeping bag) and a wind or moisture barrier for the best result. If you’re alert and shivering, you can typically rewarm without medical help.
Anxiety and the Adrenaline Response
Strong emotions, especially fear, shock, or intense anxiety, can trigger shivering that has nothing to do with temperature. This happens through your fight-or-flight system. When your brain perceives a threat, it floods your body with adrenaline. That surge causes a cascade of physical effects: racing heart, sweating, muscle tension, and sometimes visible trembling or shivering. The tiny muscles around each hair follicle also contract, giving you goose bumps.
This response is completely automatic. You don’t choose to start it and you can’t simply decide to stop it. The shivering typically subsides once the perceived threat passes and adrenaline levels drop. If you’re shivering during a panic attack or period of intense stress, slow breathing and removing yourself from the stressful situation can help your nervous system calm down faster.
Low Blood Sugar
When blood glucose drops below about 70 mg/dL, your body releases stress hormones to push sugar back into your bloodstream. That hormonal surge produces shakiness and trembling that can feel identical to shivering. You’ll usually also notice sweating, a fast heartbeat, lightheadedness, or irritability. This is most common in people with diabetes who take insulin or certain medications, but it can happen to anyone who hasn’t eaten in a long time, has exercised heavily, or has been drinking alcohol without food.
Eating or drinking something with fast-acting sugar, like juice, glucose tablets, or regular soda, typically resolves the shaking within 10 to 15 minutes.
Thyroid Problems
Your thyroid gland sets the pace of your metabolism, which is your body’s primary source of internal heat. When thyroid hormone levels are too low (hypothyroidism), your cells burn less fuel and produce less warmth. The result is a persistent sensitivity to cold that can leave you shivering in temperatures that feel perfectly comfortable to everyone else. About 4.3% of people have a mild, often undiagnosed form of low thyroid function.
Cold intolerance from hypothyroidism tends to be chronic rather than sudden. If you’ve noticed that you’re always the coldest person in the room, you’re more fatigued than usual, your skin is dry, or you’ve gained weight without changing your habits, low thyroid function is worth investigating with a simple blood test.
Medication Reactions
Certain medications can cause shivering as a side effect, particularly when they affect serotonin levels in the brain. When serotonin builds up too much, a condition called serotonin syndrome can develop. Shivering is one of its hallmark signs, alongside a rapid heartbeat, sweating, agitation, and confusion. This is most likely to happen when two or more serotonin-affecting drugs are combined. Common culprits include antidepressants (SSRIs and SNRIs), certain pain medications like tramadol and fentanyl, the herbal supplement St. John’s wort, and even some antibiotics.
If you’ve recently started a new medication or combined medications and can’t stop shivering, especially with a fast heartbeat or confusion, this needs prompt medical attention. Serotonin syndrome can escalate quickly.
Shivering After Surgery
If you’re reading this after a recent procedure, post-anesthetic shivering is remarkably common. Up to 60% of patients shiver after general anesthesia, and about 55% after spinal or epidural anesthesia. It happens partly because anesthesia disrupts your brain’s temperature regulation and partly because operating rooms are cool and your body loses heat during surgery. Younger patients and those who had longer procedures are at higher risk. Hospital staff expect this and typically treat it with warm blankets and, if needed, medication. It almost always resolves within an hour or two.
When Shivering Points to Something Serious
Most shivering resolves on its own once you warm up, eat, calm down, or let a fever run its course. But certain patterns deserve attention. Shivering with a high fever and confusion could indicate a severe infection. Shivering that suddenly stops in a very cold person suggests dangerous hypothermia. Shivering alongside a racing heart, sweating, and agitation after starting new medications may signal serotonin syndrome. And chronic, unexplained cold sensitivity paired with fatigue could point to a thyroid issue that’s easily treatable once diagnosed.