High blood pressure does not cause fever. The two are regulated by overlapping circuits in the brain, which is why they sometimes show up together during a medical crisis, but elevated blood pressure on its own will not push your body temperature above normal. When someone has both hypertension and a fever at the same time, a separate process is almost always responsible for the temperature spike, whether that is an infection, a hormonal emergency, a drug reaction, or damage to the brain’s thermostat itself.
Why People Confuse the Two
It is easy to see why the question comes up. A person in the middle of a hypertensive episode can feel flushed, sweaty, and overheated. Those sensations mimic what happens during a fever, and if someone checks their blood pressure and temperature at the same moment, both numbers might be higher than expected. But flushing and sweating during a blood pressure spike are caused by the sympathetic nervous system revving up blood flow to the skin, not by an actual rise in core body temperature. The feeling of being warm is real; a true fever, defined as a core temperature above roughly 38 °C (100.4 °F), is not a feature of garden-variety hypertension.
Part of the confusion also stems from the fact that blood pressure and body temperature share regulatory real estate in the brain. A small structure in the hypothalamus called the median preoptic nucleus (MnPO) processes signals from both temperature sensors in the skin and pressure sensors in the arteries. It then coordinates responses ranging from shivering and sweating to the constriction or dilation of blood vessels and changes in heart rate.1PubMed. The median preoptic nucleus: A major regulator of fluid, temperature, sleep, and cardiovascular homeostasis Because this same cluster of neurons is involved in both temperature regulation and blood pressure control, disruptions in one system can sometimes ripple into the other. But that is different from saying that hypertension itself generates a fever. The shared wiring creates the potential for overlap during a crisis; it does not mean a high reading on a blood pressure cuff will move the mercury on a thermometer.
What Fever Actually Does to Blood Pressure
If anything, the relationship tends to run in the opposite direction. When your body produces a genuine fever in response to infection or inflammation, blood pressure often dips rather than rises. A study in neurosurgical intensive-care patients found that for every 1 °C increase in body temperature, systolic blood pressure dropped by about 4 mmHg, while pulse rate climbed by roughly 7 beats per minute.2PubMed. Effects of fever on haemodynamic parameters in neurosurgical intensive care unit patients That makes physiological sense: fever triggers vasodilation so the body can dump heat through the skin, which lowers the resistance blood has to push against and pulls systolic pressure down. Heart rate rises to compensate for the drop in vascular resistance and to keep blood flowing to vital organs.
Diastolic pressure, interestingly, tends to hold steady or inch upward during fever, but the overall picture is that fever is a vasodilator, not a vasoconstrictor. So a person running a temperature of 39 °C is more likely to have lower-than-usual systolic blood pressure than higher. The idea that fever drives blood pressure up is, for most people, simply backwards.
Medical Emergencies Where Both Show Up at Once
There are a handful of genuine medical emergencies in which sky-high blood pressure and high body temperature appear at the same time. These are situations where neither one is causing the other; instead, a third process is driving both. Recognizing the difference matters because the treatment targets that underlying process, not the blood pressure or the temperature in isolation.
Thyroid Storm
When the thyroid gland floods the body with hormones in a crisis known as thyroid storm, the result is a dramatic acceleration of metabolism. Patients classically present with fever, heart rate that climbs far beyond what the temperature alone would explain, and blood pressure that can swing wildly, often with a very high systolic number and a relatively low diastolic number (a wide pulse pressure).3SAEM. Thyroid Storm Thyroid storm is life-threatening and requires emergency treatment aimed at blocking excess thyroid hormone production, not simply lowering blood pressure or temperature individually. The fever here comes from metabolic overdrive, not from the elevated blood pressure.
Autonomic Dysreflexia
People living with spinal cord injuries above the mid-thoracic level are susceptible to a condition called autonomic dysreflexia. A painful or irritating stimulus below the level of injury, something as simple as a full bladder or tight clothing, can trigger a massive, uncontrolled sympathetic response. Blood pressure shoots up dangerously, and the body’s normal thermoregulatory mechanisms break down: profuse sweating may appear above the level of injury while the skin below remains dry, and core temperature can become erratic.4PubMed Central. Evaluation and Management of Autonomic Dysreflexia and Other Autonomic Dysfunctions: Preventing the Highs and Lows In this scenario, the temperature dysregulation and the blood pressure spike share a common cause: the spinal cord can no longer coordinate the autonomic nervous system properly. Removing the triggering stimulus is the first step in bringing both numbers down.
When the Brain’s Thermostat Gets Damaged
One situation where high blood pressure and fever can be genuinely intertwined is a catastrophic event inside the brain itself. A hemorrhagic stroke, for instance, can both raise blood pressure (the brain tries to maintain blood flow around a bleed by driving pressure higher) and destroy the temperature-regulation centers in the hypothalamus. When blood from a brain hemorrhage extends into the brain’s ventricular system, it can stimulate prostaglandin release and compress the temperature-sensitive neurons in the brainstem or hypothalamus, producing what clinicians call a “central fever.”5PubMed Central. Central fever in patients with spontaneous intracerebral hemorrhage: predicting factors and impact on outcome
Central fever is distinct from an infection-related fever: it typically does not respond well to standard fever-reducing medications like acetaminophen or ibuprofen, because the problem is not excess prostaglandin production in the bloodstream but direct damage to the brain’s thermostat. In these patients, blood pressure is also extremely high, but neither condition is causing the other. Both are consequences of the bleed. This is a critical distinction in the intensive care unit, because treating the fever as though it were from an infection (with antibiotics and antipyretics) will miss the mark, and treating the blood pressure in isolation ignores the damaged thermoregulation that also needs aggressive cooling interventions.
Drugs That Raise Both Pressure and Temperature
Certain substances and medications can push blood pressure and body temperature up simultaneously, creating a situation that might look like hypertension is causing the fever. The mechanism varies depending on the substance.
Stimulant drugs are a classic example. Cocaine delays the body’s normal cooling responses by shifting the temperature threshold at which sweating and skin blood vessel dilation kick in. In controlled experiments, cocaine raised the core temperature threshold for vasodilation and sweating by about 0.3 °C compared to a control, and it paradoxically blunted the person’s subjective awareness that they were overheating.6Annals of Internal Medicine. Mechanism of cocaine-induced hyperthermia in humans At the same time, cocaine’s sympathomimetic effects constrict blood vessels and accelerate the heart, spiking blood pressure. The result is a person who is simultaneously hypertensive, hyperthermic, and unaware of how hot they are getting. The danger compounds in warm environments or during physical exertion.
Some psychiatric medications can also trigger both effects. Antipsychotics like clozapine and olanzapine have been documented to cause fevers ranging from mild (around 37.8 °C) to dangerously high (above 40 °C), with accompanying increases in inflammatory signaling molecules like interleukin-6.7PubMed Central. Fever development in neuroleptic malignant syndrome during treatment with olanzapine and clozapine In the most severe form, neuroleptic malignant syndrome, patients develop extreme muscle rigidity, high fever, and cardiovascular instability including elevated blood pressure. Again, the blood pressure is not causing the fever. Both are driven by the drug’s disruption of dopamine signaling and the resulting cascade of autonomic dysfunction.
Heat Stress and the Cardiovascular System
Even without any medication or disease, simple environmental heat can create a situation where blood pressure and temperature interact in ways people find confusing. Passive whole-body heating, just sitting in a very hot room without exercising, can push heart rate above 100 beats per minute and drive cardiac output up to about 13 liters per minute, which is a substantial increase from the roughly 5 liters at rest.8PubMed Central. Heat stress and baroreflex regulation of blood pressure The body does this to keep blood pressure adequate in the face of massive vasodilation in the skin. In a healthy person, blood pressure may actually fall slightly despite the heart working harder, because the blood vessels are so widely open to shed heat. But in someone whose cardiovascular system is already strained, particularly an older adult with stiff arteries or existing heart disease, the compensatory mechanisms can fail. That person might experience both a rise in core temperature and a dangerous blood pressure swing.
This is part of why heat waves are so lethal for people with cardiovascular disease. The body’s attempt to cool itself demands a level of cardiac output that a compromised heart cannot sustain. Blood pressure can become unstable, oscillating between dangerously high and dangerously low, while core temperature climbs because the cooling system is underpowered. The practical takeaway for anyone with hypertension: extreme heat is a cardiovascular stressor even if you are sitting still, and the symptoms can mimic both a blood pressure crisis and a fever simultaneously.
The Circadian Connection
Blood pressure and body temperature both follow a 24-hour cycle driven by the body’s internal clock. Core body temperature dips to its lowest point in the early morning hours and peaks in the late afternoon or evening. Blood pressure follows a broadly similar pattern, rising after waking and falling during sleep, with research showing a significant endogenous circadian rhythm in both systolic and diastolic pressure that peaks in the evening.9PubMed Central. Existence of an endogenous circadian blood pressure rhythm in humans that peaks in the evening These rhythms are coordinated by the same central clock machinery, and circadian disruption, from shift work, jet lag, or sleep disorders, can dysregulate both systems at once.10PubMed Central. Circadian clock-mediated regulation of blood pressure
This shared timing might contribute to the feeling that blood pressure and temperature are causally linked. If you take your blood pressure and temperature in the late afternoon, both are likely to be slightly higher than they were at 6 a.m. A person who is already anxious about their blood pressure might interpret a warm forehead and a higher-than-morning reading as evidence that hypertension is giving them a fever. In reality, both measurements are simply following their normal daily arc. The takeaway is mundane but useful: if you are tracking either number at home, try to measure at roughly the same time each day so you are comparing like with like.
When to Actually Worry
If you have known hypertension and you develop a genuine fever, the most likely explanation is the same as it would be for anyone else: an infection. Urinary tract infections, pneumonia, skin infections, and viral illnesses all cause fever regardless of your blood pressure status. The fever should be evaluated on its own terms, and your blood pressure medications should generally continue unless a doctor says otherwise.
There are a few situations, though, where the combination of very high blood pressure and fever together should prompt urgent evaluation:
- Sudden severe headache with fever and very high blood pressure: This combination raises concern for a central nervous system event like a hemorrhagic stroke or meningitis.
- Fever after starting a new medication: Drug-induced fever can occur with many classes of medication, including some blood pressure drugs. If a fever appears within days to weeks of starting a new prescription, tell your doctor.
- Muscle rigidity, confusion, and high temperature in someone taking psychiatric medication: This constellation suggests neuroleptic malignant syndrome and requires emergency care.
- Fever, racing heart, and tremor in someone with thyroid disease: Thyroid storm can escalate rapidly and needs immediate treatment.
Outside of these scenarios, the presence of high blood pressure does not make a fever more dangerous than it would be otherwise, and a fever does not make your blood pressure harder to manage in any lasting way. The two are physiological neighbors that share regulatory brain circuitry and circadian timing, which explains why they occasionally fluctuate in parallel, but they are not in a cause-and-effect relationship in everyday life. People with hypertension do not run fevers more often than people with normal blood pressure, and bringing blood pressure under control with medication will not change your baseline body temperature.