High blood pressure develops when the force of blood pushing against your artery walls stays elevated over time. For most people, roughly 90% of cases, there is no single cause. Instead, a combination of genetics, aging, diet, and lifestyle factors gradually pushes pressure upward. The remaining cases stem from an identifiable medical condition, a medication, or a hormonal disorder.
How Blood Pressure Is Regulated
Your body controls blood pressure through a hormonal chain reaction that starts in the kidneys. When the kidneys detect low blood flow or low sodium levels, they release an enzyme that ultimately produces a powerful vessel-constricting molecule. This molecule tightens your arteries, signals your adrenal glands to retain sodium and water, boosts activity in your nervous system, and triggers the release of hormones that hold onto fluid. Together, these effects raise blood volume and squeeze blood vessels tighter, both of which increase pressure.
In a healthy system, this process switches on when pressure drops and switches off when it normalizes. High blood pressure often involves this system staying too active, or the kidneys holding onto too much sodium, or the blood vessels losing their ability to relax. Usually several of these problems overlap.
Genetics and Family History
More than 100 genetic variations have been linked to high blood pressure. Many of these affect the hormonal system described above, while others influence how well the inner lining of your blood vessels functions. If one parent has high blood pressure, your risk is elevated. If both parents are affected, the risk climbs further. Researchers also suspect that epigenetic changes, modifications to how genes are expressed without altering the DNA itself, play a role.
Genetics alone rarely cause high blood pressure. They set the stage, making some people more sensitive to salt, more prone to stiff arteries, or less efficient at excreting sodium. Environmental factors then push susceptible people over the threshold.
Aging and Artery Stiffness
Age is the single strongest predictor. About 70% of people over 65 have high blood pressure. The reason is largely structural: the walls of your large arteries, especially the aorta, gradually lose their elastic fibers and accumulate stiffer collagen fibers. This happens independently of clogged arteries and is a normal part of aging, though it accelerates with high blood sugar and high cholesterol.
When arteries are young and flexible, they stretch with each heartbeat and absorb the force of blood being pumped out. Stiff arteries can’t do this. The full force of each heartbeat travels straight through to smaller vessels, which is why systolic pressure (the top number) tends to rise with age even when the bottom number stays normal. At the same time, the inner lining of aging arteries produces less of the molecule that signals vessels to relax, compounding the problem.
Salt, Potassium, and Fluid Balance
High sodium intake promotes fluid retention, increases blood volume, and tightens blood vessels. But the damage goes deeper than just holding onto water. Excess sodium can accumulate in skin and muscle tissue, triggering immune cells to release inflammatory signals that injure the lining of blood vessels and kidneys. Over time, this creates a cycle: sodium retention drives inflammation, which damages the kidneys’ ability to excrete sodium, which drives more retention.
Potassium works as sodium’s counterbalance. It helps your kidneys flush out sodium, relaxes blood vessel walls by improving the availability of the molecule that signals them to dilate, and dials down activity in the stress-response branch of your nervous system. Most people eat far more sodium than potassium, and this imbalance is a significant driver of high blood pressure. Fruits, vegetables, and beans are the richest dietary sources of potassium.
Alcohol Consumption
Having more than three drinks in one sitting raises blood pressure in the short term. Repeated binge drinking, defined as four or more drinks within two hours for women or five or more for men, can cause long-term elevations. Heavy use (more than three drinks daily for women, four for men) carries the greatest risk. Moderate consumption is defined as up to one drink per day for women and up to two for men, where one drink equals 12 ounces of beer, 5 ounces of wine, or 1.5 ounces of spirits.
Sleep Apnea
Obstructive sleep apnea is one of the most underdiagnosed contributors to high blood pressure. When your airway repeatedly collapses during sleep, oxygen levels drop and carbon dioxide rises. Each episode triggers a surge in your fight-or-flight nervous system. Over months and years, these nightly surges cause lasting changes in the brain regions that control baseline nervous system activity. The result is elevated stress hormones that persist into the daytime, keeping blood pressure high around the clock. If your blood pressure is resistant to treatment, sleep apnea is one of the first things to investigate.
Chronic Stress and Cortisol
Cortisol, the body’s primary stress hormone, raises blood pressure through several mechanisms. It increases the heart’s output of blood, heightens the responsiveness of blood vessels to other constricting signals, raises resistance in the kidney’s blood vessels, and suppresses the molecule that normally relaxes artery walls. Giving cortisol to people with normal blood pressure for just five days measurably raises their readings.
Chronic psychological stress keeps cortisol levels elevated for extended periods. This doesn’t mean stress is the sole cause for most people, but it can meaningfully worsen pressure that is already trending upward from other factors like genetics or diet.
Medical Conditions That Raise Blood Pressure
When a specific, identifiable condition is driving high blood pressure, it is called secondary hypertension. These cases account for roughly 5% to 10% of all diagnoses, but they matter because treating the underlying problem can sometimes resolve the blood pressure issue entirely.
Kidney-Related Causes
The kidneys are central to blood pressure regulation, so kidney problems are the most common source of secondary hypertension. Narrowing of the arteries that supply the kidneys (often from the same fatty plaques that clog heart arteries) reduces blood flow, which tricks the kidneys into activating the pressure-raising hormonal system as if the body were dehydrated. Diabetes-related kidney damage, polycystic kidney disease, and inflammation of the kidney’s tiny filtering units can all impair sodium excretion and raise pressure.
Hormonal and Gland Disorders
Several gland disorders directly elevate blood pressure. Overproduction of the hormone aldosterone causes the kidneys to retain excessive sodium and water while dumping potassium. Cushing syndrome, whether from a tumor or from long-term corticosteroid medication, floods the body with cortisol. A rare adrenal tumor called a pheochromocytoma releases surges of adrenaline, causing dramatic spikes. Both an overactive and an underactive thyroid can raise pressure, as can overactive parathyroid glands, which elevate calcium levels in the blood.
Structural Heart Defects
Coarctation of the aorta is a narrowing of the body’s main artery that is present from birth. It forces the heart to pump harder to push blood through the constriction, raising blood pressure particularly in the upper body and arms.
Medications and Substances
A surprising number of common medications can raise blood pressure, and many people take them without realizing the connection.
- Pain relievers (NSAIDs): Ibuprofen and naproxen cause the body to retain water, which can stress the kidneys and raise pressure.
- Decongestants: Pseudoephedrine and phenylephrine, found in many cold and allergy products, narrow blood vessels throughout the body, not just in the nose.
- Hormonal birth control: Pills and patches contain hormones that raise blood pressure in some people.
- Antidepressants: Several classes, including SSRIs, tricyclics, and MAO inhibitors, can contribute.
- ADHD stimulants: These can increase heart rate and blood pressure.
- Immunosuppressants: Drugs used after organ transplants are known to raise pressure.
- Herbal supplements: Licorice root, ginseng, ephedra, and guarana can all elevate readings.
Caffeine causes short-term spikes in people who don’t consume it regularly, though habitual coffee drinkers typically develop tolerance. Illicit drugs, particularly cocaine, methamphetamine, and ecstasy, can cause severe and dangerous blood pressure elevations.
Obesity, Inactivity, and Overlapping Risks
Excess body weight raises blood pressure through multiple pathways at once. It increases blood volume (more tissue requires more blood supply), promotes insulin resistance that damages blood vessel linings, worsens arterial stiffness, and makes sleep apnea more likely. Physical inactivity compounds the problem: regular exercise improves the flexibility of blood vessels, helps the kidneys excrete sodium more efficiently, and lowers resting nervous system activity.
In practice, these causes rarely operate alone. A person with a family history of hypertension who gains weight, eats a high-sodium diet, and develops sleep apnea faces compounding risks from all four sources simultaneously. This is why high blood pressure is so common, affecting nearly half of all adults, and why addressing it usually requires changes on more than one front.