High blood pressure has no single cause in most people. About 90% to 95% of cases are classified as primary hypertension, meaning the condition develops gradually from a combination of genetic, lifestyle, and age-related factors rather than one identifiable trigger. The remaining cases are secondary hypertension, where a specific medical condition or medication is directly responsible. Under current guidelines, hypertension begins at a systolic reading of 130 or a diastolic reading of 80.
Genetics and Family History
Your genes play a meaningful but incomplete role. Family studies estimate that 15% to 35% of the variation in blood pressure between people is inherited. Twin studies push that number higher, around 60% for males and 30% to 40% for females, since identical twins share the same DNA. There is no single “hypertension gene.” Instead, blood pressure is a polygenic trait, shaped by the combined effects of many small genetic variations that influence how your body handles salt, regulates hormones, and maintains blood vessel tone.
What this means in practical terms: if one or both of your parents had high blood pressure, your risk is higher, but it is not a certainty. Genes load the gun, and lifestyle factors pull the trigger.
How Aging Raises Blood Pressure
Even in people who eat well and exercise, blood pressure tends to rise with age. The reason is structural. The walls of your large arteries, especially the aorta, gradually lose their elastic fibers and replace them with stiffer collagen. This process accelerates after middle age.
Healthy arteries stretch slightly with each heartbeat, absorbing the surge of blood and then gently pushing it forward between beats. As arteries stiffen, they lose that buffering ability. The force of each heartbeat hits harder, raising the top number (systolic pressure) while the bottom number (diastolic) may stay the same or even drop. This is why isolated systolic hypertension is the most common form in older adults. It also explains why someone can have normal readings for decades and then see their numbers climb in their 60s or 70s without any obvious change in habits.
Excess Sodium and Diet
Sodium makes your body retain water. More fluid in the bloodstream means more pressure against artery walls. Most adults consume well above the recommended limit of about 2,300 milligrams per day, and much of that sodium is hidden in processed foods, restaurant meals, bread, and canned soups rather than the salt shaker on your table.
Low potassium intake compounds the problem. Potassium helps your kidneys excrete sodium. A diet low in fruits, vegetables, and legumes leaves your body less able to clear excess salt, keeping blood pressure elevated. Diets high in saturated fat and refined sugar also contribute by promoting weight gain and inflammation in blood vessel walls.
Weight and Physical Inactivity
Carrying excess weight forces your heart to pump harder to supply blood to a larger body. Fat tissue also produces hormones and inflammatory signals that stiffen arteries and promote fluid retention. The relationship is dose-dependent: the more excess weight, the greater the risk. Losing even 5 to 10 pounds can produce a measurable drop in blood pressure.
Physical inactivity contributes independently of weight. Regular aerobic exercise strengthens the heart so it can pump the same volume of blood with less effort, and it improves the flexibility of blood vessels. Sedentary living does the opposite, allowing resting heart rate and vascular resistance to creep upward over time.
Chronic Stress and the Nervous System
Your sympathetic nervous system, the “fight or flight” wiring, plays a direct role in blood pressure regulation. When it fires, your heart beats faster, your blood vessels constrict, and your kidneys hold onto sodium and water. In short bursts, this is useful. When the activation becomes chronic, it drives sustained high blood pressure.
Research from the American Heart Association shows that sympathetic overactivity is already present in the early stages of hypertension, particularly in younger patients. Over time, this constant signaling causes the walls of small arteries to physically remodel, becoming thicker relative to their inner diameter. That structural change locks in higher resistance even when the nervous system calms down. The kidneys are especially sensitive to this process: sympathetic nerves in the kidneys influence how much sodium gets reabsorbed, how much of the blood-pressure-raising enzyme renin gets released, and how much blood flow the kidneys receive.
Chronic psychological stress, poor sleep, and conditions like sleep apnea all amplify sympathetic drive. People with chronic kidney disease show progressively higher sympathetic activation as the disease advances, creating a feedback loop where kidney damage raises blood pressure, which in turn damages the kidneys further.
Alcohol Consumption
A large meta-analysis published in the AHA’s journal Hypertension found that even small amounts of alcohol raise systolic blood pressure in a direct, linear relationship with no safe threshold. Drinking as little as one standard drink per day (about 12 grams of alcohol) was associated with an average systolic increase of 1.25 mm Hg compared to nondrinkers. That may sound small, but across a population it translates into a meaningful increase in heart attacks and strokes. The more you drink, the higher the effect, and there is no amount that appears protective for blood pressure specifically.
Medications That Raise Blood Pressure
Several common medications can push blood pressure up, sometimes enough to tip a borderline reading into hypertension territory.
- Pain relievers (NSAIDs): Ibuprofen and naproxen cause the body to retain water and can interfere with kidney function, raising blood pressure. This is especially relevant for people who take them regularly for arthritis or chronic pain.
- Decongestants: Pseudoephedrine and phenylephrine, found in many cold and allergy products, work by narrowing blood vessels in the nasal passages. That narrowing happens throughout the body, increasing pressure.
- Hormonal birth control: Pills and patches containing estrogen can raise blood pressure in some people. The risk is higher in women over 35, those who smoke, or those who are overweight.
- Certain antidepressants: Several classes of antidepressants, including older tricyclics, MAO inhibitors, and some SSRIs, can elevate blood pressure by altering how the brain processes signaling chemicals.
- Stimulants: Medications prescribed for ADHD can increase heart rate and blood pressure.
- Immunosuppressants: Drugs used after organ transplants or for autoimmune conditions can raise blood pressure through effects on the kidneys.
Illicit stimulants like cocaine, methamphetamine, and MDMA can cause severe, sudden spikes in blood pressure and pose immediate cardiovascular danger.
Medical Conditions Behind Secondary Hypertension
When a single identifiable condition is driving high blood pressure, treating that condition can sometimes resolve the hypertension entirely. The most common causes, roughly in order of frequency:
- Kidney disease: Damaged kidneys struggle to filter fluid and regulate sodium, leading to volume overload and higher pressure. Kidney disease is both a cause and a consequence of hypertension.
- Primary aldosteronism: The adrenal glands overproduce a hormone called aldosterone, which tells the kidneys to retain sodium and water. This condition is more common than previously thought and is now recognized in up to 10% of people with resistant hypertension.
- Sleep apnea: Repeated drops in oxygen during sleep trigger surges in sympathetic nervous system activity. People with untreated sleep apnea often have blood pressure that stays elevated even during sleep, when it would normally dip.
- Thyroid disorders: Both an underactive and overactive thyroid can raise blood pressure through different mechanisms. An underactive thyroid increases vascular resistance, while an overactive thyroid increases heart rate and cardiac output.
- Adrenal tumors: Rare tumors called pheochromocytomas produce bursts of adrenaline, causing dramatic spikes in blood pressure along with headaches, sweating, and rapid heartbeat.
- Cushing syndrome: Excess cortisol, whether from an adrenal problem or long-term steroid use, raises blood pressure through fluid retention and vascular changes.
Smoking and Tobacco
Every cigarette causes a temporary spike in blood pressure that lasts about 20 to 30 minutes. Nicotine stimulates the release of adrenaline, which constricts blood vessels and forces the heart to work harder. Over years, the chemicals in tobacco smoke also damage the inner lining of arteries, making them stiffer and more prone to plaque buildup. This accelerates the same arterial stiffening that happens naturally with aging, effectively making blood vessels “older” than they should be.
Why Multiple Factors Matter
For most people with high blood pressure, no single item on this list is the sole cause. A person might inherit a modest genetic predisposition, gain weight in their 40s, deal with work stress that keeps their sympathetic nervous system revved up, take ibuprofen for a bad knee, and drink a couple of glasses of wine each evening. None of those factors alone would necessarily cause hypertension, but layered together they push blood pressure past the threshold. This is also why lifestyle changes, even modest ones, can be so effective: removing or reducing any single contributor lowers the total pressure load on your cardiovascular system.