High blood pressure develops when the force of blood pushing against your artery walls stays too high over time. In roughly 85% to 90% of adults with hypertension, there’s no single identifiable cause. Instead, a combination of genetics, diet, body weight, and aging work together to push pressure upward. The remaining 10% to 15% of cases stem from a specific underlying condition, like kidney disease or a hormonal disorder.
How Blood Pressure Is Classified
The 2025 guidelines from the American Heart Association and American College of Cardiology define four categories. Normal blood pressure is below 120/80. Elevated blood pressure falls between 120 and 129 for the top number, with the bottom number still under 80. Stage 1 hypertension starts at 130/80, and Stage 2 begins at 140/90 or higher. If your top and bottom numbers fall into different categories, the higher category applies.
Genetics and Family History
Family and twin studies estimate that 30% to 50% of blood pressure variation comes from inherited genes. That doesn’t mean hypertension is inevitable if your parents had it, but it does mean your baseline risk is higher. The genetic contribution isn’t one single gene. Hundreds of small genetic variations each nudge blood pressure slightly, and their combined effect interacts with everything else on this list.
How Your Body Regulates Pressure
Your kidneys play a central role. When blood pressure drops, your kidneys release an enzyme called renin, which triggers a chain reaction: your liver produces a protein that renin breaks apart, and your lungs then convert the result into an active hormone that narrows the muscular walls of small arteries. That same hormone tells your adrenal glands to release aldosterone, which signals your kidneys to hold onto sodium. More sodium means more water retention, which increases blood volume. All of this raises pressure back up.
In a healthy system, this cycle turns on when pressure is low and turns off when it normalizes. But when the system stays overactive, whether from excess sodium in your diet, kidney damage, or hormonal imbalances, blood pressure climbs and stays elevated.
Salt, Potassium, and Fluid Balance
Sodium gets the most attention, and for good reason. When you eat more salt than your kidneys can efficiently clear, your body retains extra water to dilute it. That extra fluid increases blood volume and puts more pressure on artery walls. But the story isn’t just about sodium. Potassium actively works in the opposite direction. It relaxes blood vessel walls by changing the electrical activity of muscle cells lining the arteries, causing them to widen. People with “salt-sensitive” blood pressure tend to respond especially well to increasing potassium, partly because potassium helps the kidneys excrete more sodium.
Most people eat far more sodium and far less potassium than their bodies are designed to handle. Correcting that imbalance, through more fruits, vegetables, and beans and less processed food, is one of the most effective dietary changes you can make.
How Excess Weight Raises Pressure
Carrying extra body fat doesn’t just make the heart work harder to supply a larger body. Fat tissue produces leptin, a hormone best known for regulating appetite. Leptin also acts on the brain to ramp up activity in the sympathetic nervous system, the “fight or flight” branch that speeds up heart rate and tightens blood vessels. In people with obesity, leptin levels are chronically elevated, and this sustained sympathetic activation drives up blood pressure day after day. Leptin specifically activates nerve signals to the kidneys, prompting them to retain more sodium and fluid, compounding the effect.
Arterial Stiffness and Aging
Even in people who eat well and stay active, blood pressure tends to rise with age. The elastic fibers in your large arteries gradually break down over decades and get replaced by stiffer collagen. When arteries lose their ability to stretch and absorb each heartbeat, the top number (systolic pressure) climbs while the bottom number may stay the same or even drop. This is why isolated systolic hypertension, a high top number with a normal bottom number, is the most common pattern in people over 60.
Sleep Apnea
Obstructive sleep apnea is one of the most underrecognized contributors to high blood pressure. When your airway collapses repeatedly during sleep, oxygen levels drop and carbon dioxide spikes. Each episode triggers a surge of adrenaline and sympathetic nervous system activity. Over time, these nightly surges don’t stay confined to sleep. Stress hormone levels remain elevated into the daytime, keeping blood pressure high around the clock. If your blood pressure is hard to control despite medication, or if you snore heavily and wake feeling unrested, sleep apnea may be a hidden factor.
Medical Conditions That Cause Hypertension
When a specific disease drives blood pressure up, it’s called secondary hypertension. Treating the underlying condition can sometimes resolve the blood pressure problem entirely.
Kidney Disease
The kidneys filter blood and regulate fluid balance, so damage to them directly affects pressure. Diabetes is the most common culprit, gradually destroying the kidneys’ filtering units. Polycystic kidney disease, an inherited condition where cysts crowd out healthy tissue, also raises pressure. Narrowing of the arteries that supply the kidneys (renovascular hypertension) tricks the kidneys into thinking pressure is too low, triggering them to retain more salt and water even when overall pressure is already high.
Hormonal Disorders
Several gland problems can push blood pressure up. Aldosteronism occurs when the adrenal glands overproduce aldosterone, causing the kidneys to hoard sodium and water while dumping potassium. Cushing syndrome involves excess cortisol, either from a tumor or long-term steroid medication use. A rare adrenal tumor called a pheochromocytoma floods the body with adrenaline, causing dramatic blood pressure spikes. Overactive parathyroid glands raise calcium levels in the blood, which also triggers higher pressure.
Structural and Other Causes
Coarctation of the aorta, a narrowing of the body’s main artery present from birth, forces the heart to pump harder to push blood past the obstruction. Pregnancy can also cause or worsen hypertension, sometimes leading to preeclampsia, a serious condition that develops after 20 weeks.
Medications and Substances
A number of common medications can raise blood pressure, sometimes enough to push someone from normal into the hypertensive range. Pain relievers like ibuprofen and naproxen cause the body to retain water and can affect kidney function. Decongestants containing pseudoephedrine or phenylephrine narrow blood vessels throughout the body, not just in the nose. Hormonal birth control raises blood pressure in some people, with higher risk if you’re over 35, overweight, or a smoker.
Several classes of antidepressants can also contribute, including SSRIs, tricyclics, and MAO inhibitors. Stimulant medications used for ADHD increase heart rate and can raise pressure. Immunosuppressant drugs affect the kidneys in ways that elevate pressure, and some cancer therapies that target blood vessel growth have the same effect.
Caffeine causes short-term spikes in people who don’t consume it regularly. Herbal supplements including licorice root, ginseng, ephedra, and guarana can interfere with blood pressure as well. Illicit stimulants like cocaine, methamphetamine, and ecstasy cause dangerous, sometimes sudden increases.
Physical Inactivity and Chronic Stress
Regular physical activity keeps arteries flexible, helps the kidneys process sodium efficiently, and reduces sympathetic nervous system activity. Without it, these protective effects disappear. Sedentary living also promotes weight gain, which feeds back into the leptin-driven cycle described above.
Chronic psychological stress keeps your body in a low-grade fight-or-flight state, with elevated heart rate and constricted blood vessels. While a single stressful day won’t cause lasting hypertension, years of unmanaged stress contribute to sustained elevation, especially when stress leads to poor sleep, overeating, or increased alcohol use.
Alcohol
Drinking more than moderate amounts of alcohol raises blood pressure through multiple pathways. It stimulates the sympathetic nervous system, increases cortisol levels, and may impair the ability of blood vessels to relax. The effect is dose-dependent: the more you drink on a regular basis, the greater the rise. Reducing heavy drinking is one of the more reliable ways to bring elevated readings down.