Why Do I Have Chills and a Headache?

Chills and a headache appearing together almost always mean your immune system has been activated and is releasing signaling molecules called cytokines into your bloodstream. The most common trigger is a viral infection like influenza or COVID-19, but the combination can also show up with bacterial infections, certain medications, and a handful of non-infectious conditions. Understanding what drives these two symptoms to travel as a pair, and knowing which accompanying signs point toward something urgent, can help you decide whether you need rest and fluids or a trip to the emergency room.

Why These Two Symptoms Travel Together

Chills and headache feel like separate problems, but they share a common upstream cause. When your body detects an invader, immune cells release pro-inflammatory cytokines such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α). These molecules act on the hypothalamus, the brain region that controls your internal thermostat. The hypothalamus responds by raising your set-point temperature, essentially deciding your body should be warmer than it currently is. Because your actual temperature has not caught up yet, the gap between where you are and where the thermostat wants you to be triggers shivering and that bone-deep cold sensation we call chills.

At the same time, those same cytokines inflame blood vessels and pain-sensing structures inside the skull. Research on COVID-19 patients with headache found elevated levels of both pro-inflammatory and anti-inflammatory cytokines compared to COVID-19 patients without headache, suggesting that a more intense immune response drives head pain alongside the fever response.¹ So chills and headache are not two unrelated symptoms that happen to coincide. They are two outputs of the same inflammatory cascade, which is why they so often arrive together.

Common Viral Infections

The overwhelming majority of chills-plus-headache episodes come from run-of-the-mill viral infections. Influenza is the classic example. The flu tends to hit suddenly, with chills, headache, body aches, and fatigue all arriving within hours rather than building gradually over days. COVID-19 follows a similar pattern, though it often adds loss of taste or smell and can linger longer. Other common viruses that produce this combination include respiratory syncytial virus (RSV), adenovirus, and the less dramatic but very common rhinoviruses that cause “bad colds.”

Gastroenteritis viruses like norovirus and rotavirus can also cause chills and headache alongside their hallmark vomiting and diarrhea. The key point is that viral infections are self-limiting. For most otherwise healthy adults, the chills-and-headache phase resolves within a few days as the immune system gains the upper hand. Supportive care, meaning adequate fluids, rest, and over-the-counter fever reducers when comfort matters, is the standard approach.

Bacterial Infections and the Significance of Shaking Chills

Bacterial infections can also cause chills and headache, and the character of the chills matters more than many people realize. Researchers draw a distinction between ordinary chills, which are a subjective feeling of coldness, and shaking chills (sometimes called rigors), which involve visible, uncontrollable shivering so intense you cannot stop it even under a heavy blanket.² That distinction carries real diagnostic weight.

Shaking chills are strongly associated with bacteremia, meaning bacteria have entered the bloodstream. In one prospective study of hospitalized patients, those with shaking chills were roughly three-and-a-half times more likely to have a positive blood culture than those without, even after adjusting for age and sex.³ A systematic review and meta-analysis confirmed that shaking chills are one of the more useful bedside indicators doctors have for predicting whether bacteria are circulating in the blood.²

This does not mean every episode of shaking chills equals a bloodstream infection. Plenty of viral illnesses produce rigors too, especially influenza. But when shaking chills are accompanied by a high fever, confusion, rapid heart rate, or a known site of infection like a urinary tract infection or pneumonia, the probability of bacteremia goes up enough that most clinicians will draw blood cultures and start antibiotics early rather than wait.

Meningitis and Other Neurological Emergencies

Bacterial meningitis is one of the scenarios where chills and headache can signal a life-threatening emergency. The classic triad is fever, headache, and neck stiffness, but not everyone presents with all three. Chills are common early on, and the headache tends to be severe and diffuse rather than throbbing on one side. What separates meningitis from a bad flu is how quickly you deteriorate. A person with meningitis often goes from feeling lousy to looking seriously ill within hours, not days.

Other red-flag symptoms that should prompt an immediate emergency department visit when they appear alongside chills and headache include a stiff neck that makes it painful to touch your chin to your chest, a rash that does not blanch when you press on it (especially small purplish spots), confusion or difficulty staying awake, sensitivity to light so severe you cannot tolerate a normal room, and seizures. Any of these in combination with chills and headache warrants urgent evaluation. Bacterial meningitis is treatable with antibiotics, but outcomes depend heavily on how quickly treatment starts.

Medication and Treatment Reactions

Not every episode of chills and headache traces back to an infection. Some medications trigger immune-like responses that mimic what an infection does to your body. One well-documented example is the Jarisch-Herxheimer reaction, which can happen after antibiotic treatment of certain bacterial infections, particularly syphilis. When large numbers of bacteria die off quickly, fragments of their cell walls flood the bloodstream and provoke a surge of inflammatory cytokines.

In a secondary analysis of a clinical trial involving adults treated for early syphilis with benzathine penicillin G, about one in four patients experienced at least one symptom of this reaction. The most frequently reported symptoms were muscle aches, chills, weakness, feverishness, and headache. Chills specifically showed up in close to half of those who had any reaction, and they tended to cluster with feverishness, weakness, and body aches rather than appearing alone.⁴ The reaction is temporary and usually resolves within 24 hours, but it can be alarming if you are not expecting it.

Other medications that can cause chills and headache as side effects or as part of an immune response include certain chemotherapy drugs, biologic therapies used for autoimmune conditions, and blood transfusions. If you develop chills and a headache shortly after starting a new medication or receiving an infusion, that timing is worth mentioning to your doctor, because the treatment itself may be the cause rather than a new infection.

Non-Infectious Medical Conditions

A few conditions that have nothing to do with germs can produce chills and headache. Thyroid storm is one of the more dramatic examples. This is a rare but dangerous flare of an overactive thyroid gland, and it involves extreme levels of thyroid hormone flooding the body. Symptoms include a very fast heart rate, high fever, agitation, and sometimes chills, nausea, and headache. Thyroid storm is a medical emergency that requires hospital treatment with beta-blockers, antithyroid drugs, corticosteroids, and careful monitoring.⁵

Certain autoimmune conditions, especially lupus and adult-onset Still’s disease, can produce recurrent fevers with chills and headache that cycle without any identifiable infection. These are sometimes called “fevers of unknown origin” until the underlying autoimmune disorder is identified. If you keep getting episodes of chills and headache with no obvious infectious cause, and especially if you also have joint pain, unexplained rashes, or significant fatigue, mention the pattern to your doctor. The workup may need to extend beyond infectious disease testing.

Dehydration and heat exhaustion are simpler and more common non-infectious triggers. When your body overheats and then tries to reset, you can experience chills even in a warm environment, along with a headache driven by dehydration and changes in blood flow. This is especially common after prolonged exertion in hot weather or after heavy alcohol consumption, which is itself dehydrating.

How to Manage Chills and a Headache at Home

For the vast majority of cases, which are viral infections, home management is straightforward. The goal is comfort, not necessarily eliminating the fever entirely. Fever is part of the immune response, and moderate fevers do not need to be aggressively treated unless they are making you miserable or you have a condition that makes fever risky.

Acetaminophen and non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen are the standard options for bringing down a fever and easing headache pain. A review of antipyretic options found that both classes are effective at reducing temperature, and the choice between them often comes down to individual tolerance and contraindications.⁶ Ibuprofen has the added benefit of reducing inflammation, which may help more with body aches, but it can irritate the stomach and is not safe for everyone with kidney or heart conditions. Acetaminophen is gentler on the stomach but requires careful dosing to avoid liver damage, especially if you drink alcohol.

Beyond medication, staying hydrated matters more than most people appreciate. Fever increases your fluid losses, and dehydration makes headaches worse. Water, broth, and electrolyte drinks are all reasonable choices. Layering blankets during the chills phase and removing them once you start to feel warm is a better strategy than trying to bundle up continuously, because once the fever breaks and your set point drops back down, excess insulation can push your temperature uncomfortably high.

When to See a Doctor

Most chills-and-headache episodes resolve on their own within a few days and do not need medical attention. But certain combinations of symptoms shift the odds enough that waiting it out becomes risky. The following deserve prompt evaluation:

Stiff neck: Especially if bending your chin toward your chest causes sharp pain, this raises concern for meningitis.
High fever that won’t break: A temperature above 103°F (39.4°C) that does not respond to acetaminophen or ibuprofen after a reasonable dose, or that persists beyond three days, warrants a call to your doctor.
Confusion or altered behavior: If you or someone around you is disoriented, unusually drowsy, or not making sense, that suggests the infection or condition is affecting the brain.
Shaking chills with known infection: If you already have a diagnosed infection like a urinary tract infection or pneumonia and you develop rigors, the bacteria may have entered the bloodstream.³
Non-blanching rash: Small red or purple spots that do not fade when you press a glass against them can indicate meningococcal disease or other serious infections.
Immunocompromised status: If you are on chemotherapy, take immunosuppressive drugs, or have HIV with a low CD4 count, your threshold for seeking care should be lower because your body may not mount the usual warning signs of a worsening infection.

People over 65 and infants under three months also get a lower threshold. Older adults sometimes run lower baseline temperatures, so even a modest fever with chills can indicate a more serious process than it would in a younger adult. Infants can deteriorate quickly, and fever in a newborn always warrants urgent evaluation.

Chills Without Fever

Sometimes you feel genuinely chilled and have a headache, but your thermometer reads normal. This is common and does not necessarily mean something different is going on. The early phase of many infections triggers chills before the fever has fully developed, so you may catch yourself in the gap between the thermostat being reset and your temperature actually climbing. Checking again in an hour or two often reveals a fever that was not there yet on the first reading.

But chills without fever can also point to non-infectious causes. Anxiety and panic attacks can produce chills, shivering, and headache through activation of the fight-or-flight response. Low blood sugar in people with diabetes, or occasionally in people who have gone a long time without eating, can cause shaking, headache, and a cold-sweat sensation that closely mimics infectious chills. Anemia, particularly if it develops gradually, can make you feel cold and headache-prone without any fever at all.

If chills and headache keep recurring without a fever ever materializing, that pattern is worth bringing to your doctor’s attention. It may turn out to be something straightforward like chronic tension headaches combined with cold sensitivity, or it may be a clue to an underlying condition that needs investigation.

Malaria and Travel-Related Infections

If you have recently traveled to a tropical or subtropical region, chills and headache take on a different significance. Malaria is the most important infection to consider, and it classically presents with cyclical episodes of shaking chills followed by high fever, drenching sweats, and headache. The cycles correspond to waves of parasites bursting out of red blood cells, triggering massive inflammatory responses each time. Dengue fever, typhoid, and chikungunya are other travel-related infections that produce chills, headache, and fever, each with somewhat different accompanying symptoms.

The key practical point is timing. Malaria symptoms can appear anywhere from one to four weeks after a mosquito bite, so chills and headache developing a month after returning from sub-Saharan Africa or Southeast Asia should raise the question of malaria even if you took prophylactic medication. No prophylactic regimen is 100 percent effective. If you have traveled to a malaria-endemic area and develop chills, headache, and fever, tell the emergency department about your travel history before anything else, because the standard workup for febrile illness in temperate countries does not automatically include a malaria smear, and delays in diagnosis can be dangerous.

Dengue fever, by contrast, tends to produce a more constant headache (often described as pain behind the eyes), along with a distinctive rash and sometimes joint pain severe enough that it earned the nickname “breakbone fever.” It shares chills and headache with many other infections, but the combination of retro-orbital headache, rash, and recent travel to a dengue-endemic area is a useful pattern to recognize.