Chills without a fever usually mean your body is trying to generate or conserve heat, even though you don’t have an infection raising your internal thermostat. The causes range from simple things like being cold or tired to underlying conditions like thyroid problems, low blood sugar, or anxiety. Understanding what’s behind your chills depends on what else is happening in your body at the same time.
How Your Body Produces Chills
Your hypothalamus, a small region deep in your brain, acts as your internal thermostat. It constantly receives temperature signals from sensors in your skin and deeper tissues. When those sensors detect cold, your hypothalamus triggers a chain of responses: blood vessels near your skin constrict to reduce heat loss, sweating shuts off, and your muscles begin contracting rapidly. That rapid muscle contraction is shivering, and it’s your body’s most effective way to generate heat quickly.
Normally, this system activates because you’re actually cold. But several conditions can trick or disrupt this thermoregulatory system, making you feel chills even when the room is warm and your temperature reads normal.
You Might Be Fighting Off an Early Infection
One of the most common explanations is that your body is in the early stages of an immune response. When bacteria or viruses enter your system, your immune cells release signaling molecules (particularly a group called pyrogens) that tell your hypothalamus to raise its temperature set point. Your brain essentially decides your body should be warmer than it currently is, so it triggers chills and shivering to close the gap. During this ramping-up phase, you can feel intensely cold and shaky even though a thermometer still reads normal. The fever hasn’t arrived yet, but your body is already working toward one.
This “prodromal” phase can last hours or even a day or two before a measurable fever appears. It’s especially common with respiratory infections like the flu, COVID-19, and pneumonia. If your chills eventually give way to a fever, sore throat, body aches, or cough, an early infection was likely the cause.
Anxiety and the Stress Response
Stress, anxiety, and panic attacks can produce chills that feel identical to being physically cold. When your brain perceives a threat, real or imagined, it activates the fight-or-flight response. Your adrenal glands flood your bloodstream with epinephrine (adrenaline), which redirects blood away from your skin and toward your muscles and vital organs. Your skin turns pale, feels cold, and you may shiver.
This is the same mechanism that gives you “goosebumps” during a frightening moment. But in people with chronic anxiety or panic disorder, the response can be triggered frequently and without an obvious external cause. If your chills tend to come alongside a racing heart, shallow breathing, or a sense of dread, your nervous system’s stress response is a likely explanation.
An Underactive Thyroid
Your thyroid gland controls your metabolic rate, which is essentially how much heat your body produces at rest. When thyroid function drops, your metabolism slows, and you generate less internal warmth. Feeling cold when others are comfortable is one of the hallmark symptoms of hypothyroidism.
Diagnosis involves a blood test measuring thyroid-stimulating hormone (TSH). A high TSH level signals that your brain is working harder to push an underperforming thyroid. If TSH is high and the thyroid hormone T-4 is low, hypothyroidism is confirmed. Some people fall into a gray zone called subclinical hypothyroidism, where TSH is elevated but T-4 remains normal. Even in this milder form, cold sensitivity and chills can be noticeable. Other signs include fatigue, weight gain, dry skin, and sluggish thinking.
Low Blood Sugar
When your blood sugar drops below about 70 mg/dL, your body mounts an emergency response that looks a lot like the fight-or-flight reaction. You may feel shaky, sweaty, and cold all at once. This is your autonomic nervous system trying to mobilize stored energy and alert you that something is wrong.
This is most common in people with diabetes who take insulin or certain oral medications, but it can also happen if you’ve skipped meals, exercised intensely without eating, or consumed alcohol on an empty stomach. The chills and sweating from low blood sugar tend to come on quickly and resolve within 15 to 20 minutes of eating something with carbohydrates.
Hormonal Shifts and Menopause
Most people associate menopause with hot flashes, but cold flashes are equally real and less talked about. Hot flashes are a rapid heat-dissipation response involving sweating and blood vessel dilation. As your body loses heat through a hot flash, your core temperature drops. Once it crosses a lower threshold, shivering kicks in. That shivering episode is the “cold flash” many women experience immediately after a hot flash subsides.
The underlying problem is a dramatically narrowed thermoneutral zone. In women experiencing menopausal symptoms, the gap between the temperature that triggers sweating and the temperature that triggers shivering can shrink to essentially 0°C, compared to about 0.4°C in women without symptoms. This means even tiny fluctuations in core temperature, ones that would normally go unnoticed, can trigger a full chills-and-shivering response. Estrogen therapy widens this zone by raising the sweating threshold, which is why it reduces both hot and cold flashes.
Sleep Deprivation
If you’ve been sleeping poorly, your chills may have a surprisingly straightforward explanation. The neurons that regulate sleep and the neurons that regulate body temperature overlap significantly. Research at Washington University in St. Louis confirmed what earlier studies in humans had suggested: sleep deprivation makes people feel colder. In controlled experiments, sleep-deprived animals consistently sought warmer environments, and the same pattern holds in humans. Even fragmented sleep, where you wake repeatedly throughout the night without losing total hours, disrupts thermoregulation enough to make you feel chilled the next day.
This effect compounds over time. Chronic poor sleep doesn’t just make you tired; it progressively impairs your body’s ability to maintain a stable temperature, leaving you more sensitive to cold environments that wouldn’t normally bother you.
Other Common Triggers
Several additional causes are worth considering:
- Dehydration. Water helps regulate body temperature. When you’re significantly dehydrated, your body becomes less efficient at maintaining warmth, and you may feel cold even in a comfortable environment.
- Anemia. Low red blood cell counts mean less oxygen reaches your tissues, which can reduce heat production and cause persistent cold sensitivity and chills.
- Medications. Certain drugs can cause chills as a side effect. This has been documented with antibiotics, chemotherapy agents, and some medications given by infusion. If your chills started shortly after beginning a new medication, that’s worth noting.
- Intense exercise. After a hard workout, your body temperature can drop as sweat evaporates and blood flow shifts. The resulting chills are temporary but can feel alarming if unexpected.
Patterns That Point to Something Bigger
Occasional chills from a cold room, a skipped meal, or a bad night’s sleep are normal and resolve on their own. The chills that deserve medical attention are the ones that keep coming back, worsen over time, or arrive with other symptoms. Unexplained weight loss paired with chills can point to thyroid disease or other metabolic conditions. Chills with fatigue and pallor suggest anemia. Chills that always follow a meal or occur after long gaps between eating point toward blood sugar issues.
If your chills eventually produce a temperature above 104°F (40°C) or below 95°F (35°C), that requires prompt medical evaluation. The same applies to persistent chills in infants, where even a temperature above 100.4°F in a baby under three months old warrants a call to a healthcare provider.