High blood pressure develops when the force of blood pushing against your artery walls stays elevated over time, typically at or above 130/80 mmHg. In about 90% to 95% of cases, there’s no single identifiable cause. Instead, a combination of factors gradually shifts the balance of how your body manages fluid volume, artery flexibility, and nervous system signaling. The remaining cases stem from a specific underlying condition.
How Your Body Regulates Blood Pressure
Your blood pressure depends on two things: how much blood your heart pumps and how much resistance your arteries create. A built-in control system involving your kidneys, hormones, and blood vessels constantly adjusts both. When blood pressure drops, your kidneys release an enzyme that triggers a chain reaction: your small arteries narrow, your kidneys hold onto more sodium and water, and your blood volume increases. All of this pushes pressure back up.
In a healthy system, these adjustments are temporary. But when something keeps the system dialed up, whether it’s excess sodium, stiff arteries, or hormonal imbalances, blood pressure stays elevated. Over months and years, the heart and blood vessels remodel around that higher pressure, making it harder to reverse.
Sodium, Potassium, and Fluid Balance
Eating too much sodium is one of the most well-established contributors to high blood pressure, and the mechanism goes beyond simply holding onto extra water. When sodium levels rise in your blood, your body retains fluid to dilute it, which increases blood volume. But sodium also has a direct effect on artery walls. It triggers a signaling cascade in the smooth muscle cells lining your arteries that increases calcium levels inside those cells. Higher calcium causes the muscle to contract and stay contracted, narrowing the artery and raising resistance. So excess sodium raises pressure through two routes at once: more fluid in the system and tighter blood vessels carrying it.
Potassium works as a counterbalance. It helps your kidneys flush sodium out through urine, and increasing your potassium intake can measurably lower blood pressure if it’s already elevated. Most people eat well above the recommended limit of 2,300 mg of sodium per day while not getting enough potassium, which tilts the balance toward higher pressure over time.
What Happens to Arteries With Age
Aging is the single strongest predictor of high blood pressure, and the reason is structural. Your arteries contain a mix of elastic fibers (which let them stretch with each heartbeat) and collagen (which provides rigidity). Over decades, elastic fibers break down and aren’t efficiently replaced. Collagen accumulates, and cross-links form between fibers, making the artery wall progressively stiffer. Calcium deposits can build up in the wall as well, further reducing flexibility.
Beyond these structural changes, the smooth muscle cells in artery walls become stiffer on their own. Oxidative stress, particularly from overactive enzymes in mitochondria, damages these cells and accelerates the process. The cells shift toward a state that promotes inflammation, more collagen production, and impaired ability to relax. The lining of the blood vessels (endothelium) also loses some of its ability to produce signals that tell arteries to dilate. The net result is that arteries can’t absorb the pulse of each heartbeat the way they once did, so systolic pressure (the top number) climbs steadily with age.
Genetics and Family History
Hypertension runs in families. If both of your parents have high blood pressure, your risk is substantially higher than average. More than 100 genetic variations have been linked to essential hypertension so far, and the most studied ones involve the hormonal system that controls sodium retention and artery constriction. Other relevant genes affect how well the lining of your blood vessels functions.
No single gene causes high blood pressure on its own. Each variation contributes a small increase in risk, and these genetic effects interact with lifestyle factors like diet, weight, and physical activity. This is why two people with identical diets can have very different blood pressure readings, and why family history matters even when you’re doing everything else right.
Weight, Insulin, and Metabolic Health
Carrying excess weight raises blood pressure through several overlapping pathways. Fat tissue is metabolically active. It produces inflammatory signals and hormones that affect artery function and fluid balance. But one of the most important connections runs through insulin.
When your body becomes less responsive to insulin (a condition called insulin resistance, common with excess weight), your pancreas compensates by producing more of it. Chronically elevated insulin levels directly increase sodium reabsorption in the kidneys, meaning your body holds onto more fluid. High insulin also stimulates the sympathetic nervous system, the “fight or flight” branch that speeds your heart rate and constricts blood vessels. These two effects, more fluid and tighter arteries, push blood pressure up. This helps explain why blood pressure often improves significantly with even modest weight loss.
Alcohol, Sleep Apnea, and Other Contributors
Alcohol has a clear, dose-dependent relationship with hypertension. A 2024 meta-analysis found a linear increase in hypertension risk above about 12 grams of alcohol per day, roughly equivalent to one standard drink. In men, the risk increased across the entire range of consumption. In women, the elevated risk appeared above that 12-gram threshold. The more you drink beyond that point, the higher the risk climbs.
Obstructive sleep apnea is another major and often overlooked driver. When your airway repeatedly collapses during sleep, oxygen levels drop and carbon dioxide rises. Each episode triggers a burst of stress hormones and activates the sympathetic nervous system. Over time, these nightly surges cause lasting changes in how the brain regulates sympathetic activity, keeping the system in a heightened state even during the daytime. This is why people with untreated sleep apnea frequently have blood pressure that’s difficult to control with medication alone.
Physical inactivity, chronic stress, and smoking also contribute. Regular exercise improves artery flexibility and helps your body process sodium more efficiently. Chronic psychological stress keeps stress hormones elevated, which promotes sodium retention and artery constriction through many of the same pathways described above.
Medical Conditions That Directly Raise Blood Pressure
In about 5% to 10% of cases, high blood pressure is caused by a specific, identifiable condition. This is called secondary hypertension, and treating the underlying cause can sometimes resolve the blood pressure problem entirely.
Kidney disease is the most common culprit. Damaged kidneys can’t filter sodium and fluid properly, so blood volume rises. Diabetes-related kidney damage, polycystic kidney disease, and diseases affecting the kidney’s tiny filtering units can all trigger this. Narrowing of the arteries that supply blood to the kidneys (from plaque buildup or a condition called fibromuscular dysplasia) can also fool the kidneys into thinking blood pressure is too low, activating the hormonal system that raises it.
Hormonal conditions are another category. Tumors or dysfunction in the adrenal glands can cause overproduction of cortisol, adrenaline, or aldosterone, each of which raises blood pressure through different mechanisms. Thyroid problems, both overactive and underactive, can elevate blood pressure as well. Overactive parathyroid glands raise calcium levels in the blood, which triggers blood pressure increases.
Medications and Substances
Several common medications can raise blood pressure or make existing hypertension worse. Pain relievers (especially anti-inflammatory types), birth control pills, certain antidepressants, and drugs used to prevent organ transplant rejection are among the most frequent offenders. Over-the-counter decongestants containing pseudoephedrine can cause temporary but significant spikes. Some herbal supplements, including licorice root, ginseng, and ephedra, have the same effect. Stimulant drugs like cocaine and methamphetamine raise blood pressure acutely and can cause lasting cardiovascular damage with repeated use.
Pregnancy can also trigger high blood pressure in women who had normal readings before, or worsen pre-existing hypertension. Preeclampsia, a pregnancy-specific condition involving high blood pressure and organ stress, typically develops after 20 weeks and requires close monitoring.
Why It’s Usually Multiple Factors at Once
For most people, high blood pressure doesn’t come from one cause. It’s the accumulation of genetic predisposition, years of arterial wear, dietary patterns, body composition, and lifestyle habits all converging on the same cardiovascular system. A person with a strong family history might develop hypertension in their 30s with a relatively healthy lifestyle, while someone with no family history might not see elevated readings until their 60s, when age-related arterial stiffness catches up. Understanding which factors are modifiable (sodium intake, weight, alcohol, physical activity, sleep quality) and which aren’t (age, genetics) is the practical starting point for doing something about it.