Blood pressure is the force exerted by circulating blood against the walls of the body’s arteries. It is measured as two numbers: systolic pressure (the top number, when the heart beats) and diastolic pressure (the bottom number, when the heart rests). When the body is fighting an infection, such as a common cold or the flu, blood pressure readings are often temporarily higher than usual. This elevation is a consequence of the body’s physiological response to the stress of illness, initiating defenses to combat the pathogen and support increased metabolic demands.
The Body’s Stress Response to Illness
Illness triggers a defensive cascade known as the sympathetic nervous system response, often called the “fight-or-flight” mechanism. This system prepares the body for a perceived threat, causing the adrenal glands to secrete stress hormones, primarily adrenaline (epinephrine) and cortisol, into the bloodstream.
These hormones act on the cardiovascular system by causing vasoconstriction, the narrowing of small blood vessels throughout the body. This constriction increases the resistance against which the heart must pump, directly leading to a rise in blood pressure. Adrenaline also signals the heart muscle to beat faster and with greater force, further contributing to the temporary elevation in blood pressure.
The immune system’s activation causes systemic inflammation, mobilizing cells and chemical mediators to the site of infection. This inflammatory state can influence vascular tone and contribute to the heightened activity of the sympathetic nervous system. A fever also increases the body’s metabolic rate, requiring the heart to work harder to circulate oxygen and nutrients to support the immune response.
Medications and Habits That Raise Blood Pressure When Sick
Aside from the body’s internal immune processes, certain over-the-counter medications used for colds and flu can independently raise blood pressure. Decongestants, such as pseudoephedrine and phenylephrine, are a frequent culprit because they work by constricting blood vessels in the nasal passages to reduce swelling. This vasoconstrictive effect is not localized, however, and can increase blood pressure throughout the body.
This effect is concerning for individuals who already manage high blood pressure, as decongestants can push readings into a dangerous range or interfere with prescribed antihypertensive medications. Many multi-symptom cold and flu remedies contain a decongestant. Therefore, it is important to carefully read product labels for ingredients ending in “-ephrine” or “-fedrine.”
Certain pain relievers, specifically nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and naproxen, can contribute to elevated pressure. NSAIDs can cause the body to retain fluid and sodium, which increases the total blood volume and places strain on the kidneys. This fluid retention can lead to an increase in blood pressure, especially with prolonged use or high dosages.
Behavioral changes during illness further exacerbate the problem. Dehydration from fever or reduced fluid intake can thicken the blood, making it harder for the heart to pump. Poor sleep quality and fatigue also keep the sympathetic nervous system activated, preventing blood pressure from returning to a resting baseline.
When to Consult a Doctor About Elevated Blood Pressure
While a mild, temporary rise in blood pressure is expected when sick, certain readings and symptoms require immediate medical attention. A blood pressure reading that acutely reaches or exceeds 180/120 mm Hg is considered a hypertensive crisis. If a reading is recorded in this range, retake the measurement after a few minutes of rest to confirm the result.
If this high reading is accompanied by symptoms such as severe headache, chest pain, shortness of breath, sudden weakness, vision changes, or confusion, it signals a hypertensive emergency. These symptoms indicate potential organ damage and require an immediate trip to the emergency room or a call to emergency services. Do not wait for the reading to decrease on its own.
If the reading is above 180/120 mm Hg but you have no accompanying symptoms, it is considered severe hypertension, or hypertensive urgency. In this situation, contact a healthcare provider immediately for guidance on safely lowering your blood pressure, which may involve medication adjustments. Individuals with pre-existing conditions like heart failure, chronic kidney disease, or uncontrolled hypertension should consult their doctor if their blood pressure remains persistently elevated while ill.