Recurring chills usually signal that your body’s internal thermostat has been nudged off its usual set point, whether by an infection, a hormone imbalance, low iron, or even strong emotions. The experience feels the same regardless of the trigger: your muscles contract and relax rapidly, your skin prickles, and you reach for a blanket. But the causes range from completely harmless to genuinely urgent, so the real question is which category your chills fall into and what pattern should prompt a call to your doctor.
What Happens in Your Body When You Get the Chills
Chills are, at their core, your body’s way of generating heat in a hurry. When the brain decides the body is too cold relative to its current target temperature, it triggers rapid, involuntary muscle contractions. That’s shivering. The goosebump reflex tags along as a vestige from a furrier past, when raised hairs trapped insulating air. Alongside shivering, your blood vessels near the skin constrict to keep warm blood closer to your vital organs.
During a fever, the chain of events starts with signaling molecules called prostaglandins. Research in animal models shows that prostaglandin E2 acts on a specific region of the brain to reset the body’s temperature target upward, which then triggers the involuntary heat-generating responses you feel as chills and shivering.1PubMed Central. The pyrogenic mediator prostaglandin E2 elicits warmth seeking via EP3 receptor-expressing parabrachial neurons – Section: Results In other words, when you have a fever and feel freezing cold, your body is not actually cold. It has raised its thermostat and now perceives your normal temperature as too low, so it fires up every warming mechanism it has.
This distinction matters because not all chills involve a fever. Some causes reset the thermostat; others simply impair your ability to generate or retain heat. Understanding which one you’re dealing with narrows the list of possible explanations considerably.
Infections Are the Most Common Culprit
If you’re fighting a cold, the flu, COVID-19, a urinary tract infection, or any other acute infection, chills are part of the fever response. Immune cells detect the invader and release substances that push your brain’s temperature set point higher, making you feel cold at your current body temperature. The chills drive shivering, which warms you up toward the new, higher target. Once the infection is controlled and the signaling molecules clear out, the set point drops back to normal and you start sweating instead.
For most viral illnesses, the chills come and go within a few days. Bacterial infections can produce more dramatic, shaking chills, sometimes called rigors. A prospective study of hospitalized patients found that those who experienced shaking chills had roughly three and a half times the odds of having bacteria in their bloodstream compared to those without rigors.2PubMed Central. Risk of bacteremia in patients presenting with shaking chills and vomiting – Section: Shaking chills and bacteremia That doesn’t mean every episode of shivering means you have a bloodstream infection, but violent, teeth-chattering chills accompanied by high fever, especially with vomiting, deserve prompt medical evaluation.
Thyroid Problems and the Cold Sensitivity They Create
Your thyroid gland sets the metabolic pace for nearly every cell in your body, and when it underperforms, your internal furnace dims. People with an underactive thyroid often describe persistent cold sensitivity rather than episodic chills, though the experience can feel similar: you’re reaching for a sweater when nobody else in the room is uncomfortable.
Research measuring cold-induced heat production in hypothyroid patients found that restoring normal thyroid function roughly doubled the body’s ability to generate heat in response to cold.3PubMed Central. Resolution of Hypothyroidism Restores Cold-Induced Thermogenesis in Humans – Section: Results That’s a dramatic deficit. If you’re consistently chilled, tired, gaining weight without eating more, and noticing dry skin or thinning hair, a simple blood test measuring thyroid-stimulating hormone can either confirm or rule out this cause. Because hypothyroidism develops gradually, many people chalk up the cold sensitivity to aging or their environment and don’t mention it to a doctor for months or years.
Iron Deficiency Anemia
Iron deficiency is one of the most common nutritional deficiencies worldwide, and it has a surprisingly direct effect on your ability to stay warm. When you don’t have enough iron, your red blood cells can’t carry oxygen as efficiently, and that oxygen shortfall affects heat-generating tissues.
The connection works through at least two pathways. First, anemia reduces the amount of oxygen delivered to muscles and other tissues that produce heat. Second, iron deficiency appears to blunt the thyroid’s response to cold, creating a hormonal bottleneck on top of the oxygen problem.4PubMed. Iron and thermoregulation: a review Animal studies have shown that when iron-deficient subjects were exposed to cold temperatures, the rise in thyroid hormones that normally drives heat production was significantly suppressed, and that restoring the red blood cell count corrected the problem even before tissue iron stores were fully replenished.5PubMed. Effect of iron-deficiency anemia on hormone levels and thermoregulation during cold exposure
In human studies, people with iron deficiency anemia exposed to cold environments showed lower skin temperatures and a reduced ability to raise their core temperature compared to people with normal iron levels.6PubMed Central. Cardiovascular and Thermal Responses to Cold Exposure During Exercise in Iron-Deficient Anemic Individuals – Section: Results If you’re getting frequent chills and also dealing with fatigue, pale skin, brittle nails, or heavy menstrual periods, iron deficiency is worth investigating. A complete blood count and a serum ferritin test can give your doctor a clear picture.
Hormonal Shifts During Menopause
Hot flashes get most of the attention around menopause, but chills are the other side of the same coin. Your body’s thermoregulatory system operates within a comfort zone between the temperature that triggers sweating and the temperature that triggers shivering. In women experiencing menopausal symptoms, that comfort zone shrinks dramatically. Research measuring these thresholds found that symptomatic postmenopausal women had virtually no gap between their sweating and shivering triggers, while women without symptoms had a comfortable buffer of about 0.4°C.7PubMed. Reduced thermoregulatory null zone in postmenopausal women with hot flashes
What this means in practice is that even a small drop in core temperature after a hot flash can push a symptomatic woman past her shivering threshold. The classic pattern is a flash of heat and sweating followed immediately by feeling cold and shivery as the body overcorrects. If your chills tend to follow hot flashes, or if they started around the time your periods became irregular, this narrowed thermoregulatory zone is the likely explanation. The fluctuations in estrogen that drive menopause are thought to be behind this effect, which is why hormone therapy often resolves both the hot flashes and the chills together.
Anxiety, Panic, and Stress
You don’t need to be physically sick or hormonally shifting to get chills. Anxiety and stress can produce them too, and they do so through the autonomic nervous system, the same wiring that controls your fight-or-flight response. When your body perceives a threat, it redirects blood flow toward your muscles and core organs and away from your skin. That redistribution of blood can leave your skin feeling cold and clammy, and if the response is strong enough, you may shiver.
A systematic review looking at thermoregulation in people with anxiety disorders found measurable differences in how their bodies managed temperature. People with social anxiety disorder showed altered blood flow patterns in their skin, and those with panic disorder experienced more intense sweating during stressful situations.8PubMed Central. A Systematic Review of Thermosensation and Thermoregulation in Anxiety Disorders While most of the research has focused on the sweating side of this equation, the underlying principle applies to chills as well. If your autonomic nervous system is chronically activated, your thermoregulatory responses become more exaggerated and less predictable. Chills during a panic attack, before a stressful presentation, or during periods of persistent worry are common and not a sign of underlying physical illness on their own.
That said, if you’re getting unexplained chills frequently and can’t tie them to obvious stressful moments, it’s worth checking for physical causes before attributing everything to anxiety. Anxiety is a real and valid cause of chills, but it should be a diagnosis of inclusion rather than a catch-all.
Getting Older Changes How You Handle Cold
If you’ve noticed that you get colder more easily than you did a decade ago, aging itself may be part of the picture. The body’s ability to generate heat in response to cold declines with age through several parallel mechanisms. Muscle mass decreases, and since muscles are a major heat source during shivering, less muscle means less warming capacity. At the same time, the activity of specialized fat tissue that generates heat without shivering also appears to decline.9PubMed. Cold-induced thermoregulation and biological aging
Older adults are also more likely to have one or more of the conditions discussed above: thyroid disorders, iron deficiency, or medications that affect thermoregulation. Blood pressure drugs, certain antidepressants, and sedatives can all interfere with the body’s ability to constrict blood vessels or generate heat. If you’ve recently started a new medication and noticed increased chilliness, that connection is worth discussing with your prescriber.
The practical concern with age-related cold sensitivity is that it can mask or overlap with more specific treatable causes. An older person who is always a bit cold may not realize that their thyroid has slipped into the underactive range, because they attribute the cold sensitivity to normal aging. A baseline check of thyroid function and iron levels is reasonable for anyone over 60 who notices a persistent shift in cold tolerance.
Cold Hands and Feet vs. Whole-Body Chills
There’s an important difference between feeling cold all over and having specific extremities that go numb, white, or blue in the cold. The former is usually about core thermoregulation. The latter may point to a vascular issue like Raynaud’s phenomenon, where the small arteries supplying the fingers and toes overreact to cold or stress and temporarily restrict blood flow far more than normal.
In Raynaud’s, the affected digits cycle through white (no blood flow), blue (deoxygenated blood), and red (blood returning) as the episode resolves. A study comparing children with primary Raynaud’s to healthy controls found clear structural differences in the tiny capillaries of the affected group, including dilated loops and microhemorrhages that were rare in healthy fingers.10Oxford Academic (Modern Rheumatology). Cold fingers under the lens: unveiling microvascular differences between children with primary Raynaud’s phenomenon and healthy individuals Primary Raynaud’s, the kind that occurs on its own without an underlying autoimmune disease, is uncomfortable but generally harmless. Secondary Raynaud’s, which is associated with conditions like lupus or scleroderma, requires closer monitoring.
If your chills are really about your hands and feet specifically, and you notice color changes in the cold, that’s a distinct problem from the systemic chills described in the rest of this article. Mention the color changes to your doctor, because the distinction between primary and secondary Raynaud’s matters for long-term management.
Emotional Chills That Have Nothing to Do With Temperature
Not all chills are about being cold. You’ve probably felt a wave of goosebumps while listening to a piece of music that moved you, watching an emotional scene in a film, or hearing a story that resonated deeply. These are sometimes called aesthetic chills or frisson, and they involve the same physical hardware as temperature-related chills, but the trigger is emotional rather than thermal.
Researchers studying these aesthetic chills describe them as a bridge between a physical sensation and a conscious emotional experience, involving reward-processing areas of the brain that also light up during other pleasurable activities.11PubMed Central. The neurobiology of aesthetic chills: How bodily sensations shape emotional experiences Interestingly, these chills can also occur in response to threatening or awe-inspiring stimuli, not just pleasant ones. The goosebumps you get during a horror movie use the same pathway.
These emotional chills are completely normal. Some people experience them more frequently or intensely than others, which seems to be related to personality traits like openness to experience. If your “chills” are really goosebumps during emotionally intense moments rather than feeling cold, there’s nothing to worry about, and no underlying condition to investigate. They’re a feature of how your brain processes meaning, not a malfunction.
Other Causes Worth Knowing About
Beyond the major categories above, a handful of other situations commonly produce chills:
- Low blood sugar: When glucose drops too low, the body releases stress hormones that can trigger shaking and chills. This is most relevant for people with diabetes using insulin or sulfonylureas, but it can happen in anyone who has gone too long without eating, particularly after intense exercise.
- Dehydration: Significant fluid loss, whether from illness, heat, or not drinking enough, impairs the body’s ability to regulate temperature. The result can be chills even in warm environments.
- Medication side effects: Some drugs directly affect thermoregulation. Opioid withdrawal is notorious for causing intense chills and goosebumps. Certain chemotherapy regimens produce chills as part of an infusion reaction. Even common medications like beta-blockers can reduce circulation to the extremities enough to make you feel colder.
- Sleep deprivation: Core body temperature naturally dips in the early morning hours, and chronic sleep loss can disrupt the circadian rhythm of this temperature cycle, sometimes producing chills at unusual times.
When Chills Deserve Medical Attention
Most chills are self-limiting and tied to something benign. But certain patterns raise the stakes enough to warrant a visit to your doctor or, in some cases, an emergency room.
Shaking chills with a high fever are the most urgent combination. As discussed earlier, rigors carry a meaningfully higher likelihood of bacterial bloodstream infection.2PubMed Central. Risk of bacteremia in patients presenting with shaking chills and vomiting – Section: Shaking chills and bacteremia If the shaking is violent enough that you can’t hold a cup, especially alongside vomiting, confusion, or a fever above 103°F (39.4°C), seek medical care the same day. People with weakened immune systems, whether from chemotherapy, organ transplant medications, or HIV, should have an even lower threshold for seeking evaluation when chills accompany fever.
Chills without a fever that recur for weeks are a different kind of concern. They’re less acutely dangerous but may point to an underlying condition that’s worth identifying. If you’re also experiencing fatigue, unintentional weight changes, hair thinning, or heavy periods, the combination suggests a metabolic or nutritional cause like thyroid disease or iron deficiency. If the chills come with night sweats and unexplained weight loss, your doctor may want to rule out lymphoma or other chronic conditions where chills are an early symptom.
A few other red flags worth remembering: chills that always occur at a predictable time after exposure to a specific medication or infusion, chills accompanied by a rash or joint pain, and chills that seem to cycle on a regular schedule (which in some parts of the world raises the question of malaria). In each of these cases, the chills are a useful signal, not just a nuisance, and bringing them to your doctor’s attention helps steer the workup in the right direction.
Practical Steps Before the Doctor’s Visit
If you’ve decided the chills are persistent enough to mention at your next appointment, a few things make the conversation more productive. Track the timing: do they happen at the same time each day, after meals, during exercise, or seemingly at random? Note whether they come with fever (a thermometer reading beats a guess) and how long each episode lasts. Write down any other symptoms that cluster with the chills, even ones that seem unrelated, since fatigue, hair changes, mood shifts, and menstrual irregularities all help narrow the differential.
Bring a list of your medications and supplements, including anything you’ve started or stopped in the past few months. And if you have recent lab work, bring that too. For most people with unexplained recurring chills, the initial workup is straightforward: a complete blood count to check for anemia, a thyroid panel, and basic metabolic labs. These inexpensive tests cover a wide swath of the treatable causes, and normal results are reassuring enough to shift the conversation toward less common possibilities or lifestyle factors.