Hypertension, or high blood pressure, is caused by a combination of genetic predisposition, lifestyle factors, and changes in how your body regulates fluid balance and blood vessel tone. In about 90% to 95% of cases, there is no single identifiable cause. The remaining 5% to 10% of cases stem from a specific underlying condition, such as kidney disease or a hormonal disorder.
Blood pressure is classified as normal when it falls below 120/80 mm Hg. Stage 1 hypertension begins at 130/80, and Stage 2 starts at 140/90, according to the 2025 guidelines from the American Heart Association and American College of Cardiology.
Primary Hypertension: The Most Common Type
The vast majority of people with high blood pressure have what’s called primary (or essential) hypertension. This means no single disease or defect is driving the numbers up. Instead, blood pressure creeps higher over years as multiple factors interact: your genes, your diet, your weight, your stress levels, and the gradual aging of your blood vessels.
Family studies estimate that genetics account for 15% to 35% of the variation in resting blood pressure. Twin studies push that number higher, to roughly 60% in men and 30% to 40% in women. That genetic contribution doesn’t mean hypertension is inevitable if it runs in your family, but it does mean some people’s blood pressure is more sensitive to salt, weight gain, or stress than others.
How Your Body Regulates Blood Pressure
Your blood pressure depends on two things: how hard your heart pumps and how much resistance your arteries put up against that flow. Several systems keep these in balance, and when they malfunction, pressure rises.
One key system is a hormonal chain reaction that controls fluid balance and blood vessel width. When your kidneys sense low blood flow, they release a signal that ultimately produces a hormone called angiotensin II. This hormone tightens blood vessels and tells your kidneys to hold onto salt and water, both of which raise blood pressure. In people with hypertension, this system is often overactive, keeping pressure elevated even when the body doesn’t need it.
Your nervous system plays a parallel role. The “fight or flight” branch speeds up your heart rate, narrows your blood vessels, and reduces how much blood your veins can hold. Chronic overactivation of this system, whether from stress, obesity, or sleep disorders, keeps blood pressure persistently high rather than letting it drop back down between stressful moments.
How Sodium and Potassium Affect Blood Pressure
Sodium and potassium work as a pair in your kidneys. When you eat a lot of salt and not enough potassium, your kidneys retain more sodium and water, expanding the volume of fluid in your blood vessels and pushing pressure up.
Potassium counteracts this in several ways. It prompts the kidneys to flush out more sodium, a process called natriuresis. It also directly relaxes the smooth muscle cells lining your artery walls, helping them widen. When potassium intake is low, the kidneys ramp up salt reabsorption, and blood pressure rises as a result. When potassium intake is high, that salt-retaining mechanism is suppressed and blood vessels become less stiff.
This is why dietary advice for blood pressure focuses on both sides of the equation: eating less sodium and eating more potassium-rich foods like bananas, potatoes, beans, and leafy greens.
How Excess Weight Raises Blood Pressure
Obesity is one of the strongest modifiable risk factors for hypertension, and the connection goes well beyond carrying extra mass. Fat tissue produces leptin, a hormone that normally helps regulate appetite. Leptin also activates the sympathetic nervous system, raising levels of stress hormones like norepinephrine and epinephrine. In people with obesity, leptin levels are chronically high. The appetite-suppressing effect of leptin weakens over time, but its blood-pressure-raising effect does not. The result is sustained sympathetic overdrive that keeps blood pressure elevated.
Leptin also triggers inflammation in blood vessel walls and promotes the release of a potent vessel-constricting substance from the cells lining your arteries. These effects compound the direct pressure increase from sympathetic activation, making obesity-related hypertension particularly stubborn to treat with lifestyle changes alone.
Arterial Aging and Stiffness
As you age, the elastic fibers in your artery walls gradually break down and are replaced by stiffer collagen. This process is the primary reason blood pressure tends to rise with age, even in people who maintain a healthy weight and diet.
Healthy arteries stretch with each heartbeat, absorbing some of the force before the blood reaches smaller vessels. When arteries stiffen, they can no longer do this effectively, and the systolic number (the top number) climbs while the diastolic number may stay the same or even drop. This pattern, called isolated systolic hypertension, is extremely common in adults over 60.
Several things accelerate arterial stiffening beyond normal aging. Chronic high blood sugar promotes collagen cross-linking, essentially gluing arterial walls into rigid structures. High cholesterol drives the breakdown of elastic fibers. Nicotine triggers collagen production and activates enzymes that degrade elastin. All of these processes are additive, which is why people with diabetes, high cholesterol, and smoking histories tend to develop more severe hypertension earlier in life.
Sleep Apnea and Blood Pressure
Obstructive sleep apnea is one of the most underrecognized contributors to high blood pressure. During sleep, the airway collapses repeatedly, cutting off oxygen for seconds to over a minute at a time. Each episode triggers a surge in sympathetic nervous system activity and a spike in stress hormones. Over months and years, these nightly surges cause lasting changes in the brain regions that control blood vessel tone, keeping the sympathetic system running hot even during the daytime.
Poor sleep quality and short sleep duration independently contribute to arterial stiffness, impaired blood vessel relaxation, and insulin resistance, all of which push blood pressure higher. People with resistant hypertension (blood pressure that doesn’t respond well to three or more medications) are frequently found to have untreated sleep apnea.
Secondary Hypertension: An Identifiable Cause
In 5% to 10% of cases, high blood pressure has a specific, treatable cause. This is called secondary hypertension, and it’s worth considering when blood pressure develops before age 30, rises suddenly after being stable, or doesn’t respond to standard treatment.
Kidney Disease
The kidneys are central to blood pressure regulation, so damage to them from any source can raise pressure. Diabetes is the most common culprit: high blood sugar injures the kidneys’ filtering system over time, leading to salt and fluid retention. Polycystic kidney disease, an inherited condition where cysts crowd out normal kidney tissue, is another frequent cause. Narrowing of the arteries feeding the kidneys (renovascular hypertension) reduces blood flow and tricks the kidneys into activating the hormonal system that raises blood pressure.
Hormonal Disorders
The adrenal glands sit on top of the kidneys and produce hormones that directly influence blood pressure. In a condition called aldosteronism, the glands overproduce aldosterone, a hormone that tells the kidneys to retain salt and water while flushing out potassium. Cushing syndrome, caused by excess cortisol production, also raises blood pressure. Both conditions are surgically or medically treatable, and blood pressure often improves significantly once the hormonal imbalance is corrected.
Medications and Substances That Raise Blood Pressure
Several common over-the-counter and prescription medications can raise blood pressure enough to push someone from normal into the hypertensive range, or to make existing hypertension harder to control.
- Pain relievers (NSAIDs): Ibuprofen (Advil) and naproxen (Aleve) cause the kidneys to retain sodium and water. Regular use can raise blood pressure noticeably.
- Decongestants: Pseudoephedrine and phenylephrine, found in many cold and sinus products, constrict blood vessels.
- Hormonal birth control: Pills and devices containing hormones raise blood pressure in some people.
- Antidepressants: Several classes, including SSRIs, tricyclics, and MAO inhibitors, can increase blood pressure.
- Stimulants: ADHD medications, caffeine in high doses, and illicit drugs like cocaine and amphetamines all activate the sympathetic nervous system.
- Herbal supplements: Licorice root, ephedra, ginseng, and guarana have documented blood-pressure-raising effects.
If you take any of these regularly and have elevated blood pressure, the medication itself may be part of the problem. Switching to an alternative or adjusting the dose can sometimes bring numbers back into a healthy range without adding a blood pressure medication.