High blood pressure develops when the force of blood pushing against your artery walls stays consistently too high. A reading of 130/80 mm Hg or above now qualifies as hypertension under the latest guidelines from the American Heart Association and American College of Cardiology. For about 90% of people with high blood pressure, there is no single identifiable cause. Instead, a combination of genetics, diet, aging, and lifestyle factors gradually pushes pressure upward over years.
How Your Body Controls Blood Pressure
Your blood pressure depends on two things: how hard your heart pumps and how much resistance your blood meets as it flows through your arteries. Your body has a built-in pressure regulation system centered on the kidneys. When blood flow to the kidneys drops, specialized cells release an enzyme called renin. This triggers a chain reaction: renin converts a protein in your blood into a hormone that tightens your blood vessels, signals your adrenal glands to retain sodium and water, and ramps up activity in your sympathetic nervous system. The result is higher blood volume and narrower arteries, both of which raise pressure.
This system exists to keep you alive during emergencies like dehydration or blood loss. Problems arise when it stays activated chronically, whether from kidney disease, hormonal imbalances, or other conditions that trick the kidneys into behaving as if blood flow is always too low.
Primary Hypertension: The Most Common Type
The vast majority of adults with high blood pressure have what’s called primary (or essential) hypertension. This means no single disease is driving it. Instead, it results from the cumulative effects of aging, diet, body weight, genetics, and physical inactivity interacting over decades. Primary hypertension rarely causes symptoms, which is why it often goes undetected until a routine checkup or a complication like a heart attack or stroke.
How Diet Raises Blood Pressure
The typical Western diet is one of the strongest drivers of high blood pressure, largely because of its combination of high sodium and low potassium. When you take in too much sodium and too little potassium, your kidneys retain excess fluid. That extra fluid increases blood volume, and the imbalance also causes the smooth muscle cells lining your arteries to contract. Tighter arteries plus more fluid equals higher pressure.
Potassium works as a natural counterbalance to sodium. It helps your kidneys excrete sodium and relaxes blood vessel walls. Most adults consume far more sodium and far less potassium than their bodies are designed for, and this mismatch is a major reason hypertension is so common in industrialized countries. Processed foods are the primary source of excess sodium for most people, contributing roughly 70% of daily intake.
What Aging Does to Your Arteries
As you get older, the large arteries near your heart undergo structural changes that make them stiffer. The elastic fibers in artery walls gradually fragment and break down. Your body replaces them with collagen, a tougher, less flexible protein. On top of that, sugar molecules in your blood bond to structural proteins in the artery wall, creating cross-links that further stiffen the vessel.
This stiffening has a specific signature on your blood pressure reading. The top number (systolic) rises because stiff arteries can’t expand to absorb the surge of blood from each heartbeat. The bottom number (diastolic) actually drops because the arteries don’t recoil enough to maintain pressure between beats. This pattern, called isolated systolic hypertension, is the most common form of high blood pressure in people over 50.
Sedentary Lifestyle and Arterial Stiffness
Lack of physical activity accelerates the same arterial stiffening that happens with aging. Sedentary living increases oxidative stress, a process in which unstable molecules damage the lining of your blood vessels and make artery walls less flexible. Research measuring arterial stiffness in previously inactive adults found that eight weeks of high-intensity exercise significantly reduced both oxidative stress markers and artery stiffness. Regular movement essentially acts as a natural antioxidant, protecting blood vessel flexibility and keeping pressure lower.
Chronic Stress and Blood Pressure
Short bursts of stress temporarily raise your blood pressure, and that’s normal. The concern is with chronic, unrelenting stress. Prolonged exposure to cortisol, your body’s main stress hormone, appears to raise blood pressure through its effects on blood vessels rather than by increasing heart rate. Cortisol interferes with nitric oxide, a molecule your blood vessels rely on to stay relaxed and dilated. When nitric oxide production drops, arteries tighten and resistance to blood flow increases. Research from the American Heart Association has also linked cortisol to increases in a hormone that directly constricts blood vessels, with higher levels correlating to larger rises in systolic blood pressure.
Secondary Hypertension: When a Specific Condition Is the Cause
About 10% of adults with high blood pressure have secondary hypertension, meaning another medical condition is driving the elevation. That percentage is much higher at the extremes of age: secondary causes account for 70% to 85% of hypertension cases in children under 12 and roughly 17% of cases in adults 65 and older. Clues that your high blood pressure might have a secondary cause include blood pressure that doesn’t respond to three or more medications, a sudden spike after years of stable readings, or onset before age 30.
Sleep Apnea
Obstructive sleep apnea is one of the most common secondary causes. Each time your airway collapses during sleep, your oxygen level drops. Your body’s oxygen sensors, located near the carotid arteries in your neck, respond by firing up your sympathetic nervous system, the “fight or flight” branch that raises heart rate and constricts blood vessels. In people with untreated sleep apnea, this happens dozens or even hundreds of times per night.
Over time, these repeated oxygen drops permanently recalibrate the system. The oxygen sensors become hypersensitive, staying active even during normal breathing. Meanwhile, the pressure sensors that normally tell your nervous system to calm down become blunted. The net result is a sympathetic nervous system that runs hot around the clock, not just during sleep. Stress hormones like adrenaline remain elevated, and blood vessels stay constricted. This is why people with sleep apnea often have high blood pressure that’s resistant to medication and doesn’t dip at night the way it normally should.
Kidney Artery Narrowing
When the arteries supplying your kidneys become narrowed, usually by cholesterol plaque or a condition affecting the artery wall, the kidneys receive less blood flow. They interpret this as low blood pressure throughout the body and activate the same hormonal cascade described earlier: renin release, blood vessel tightening, and sodium retention. The kidneys are essentially solving a problem that doesn’t exist, flooding your body with pressure-raising signals in response to a local blockage.
Hormonal Disorders
Several conditions involving overproduction of hormones can raise blood pressure. An adrenal gland tumor that secretes excess aldosterone causes your kidneys to retain far too much sodium and water. Overactive thyroid, overactive parathyroid, and tumors that produce adrenaline can all push blood pressure up through different mechanisms. These are less common but worth investigating when blood pressure is unusually difficult to control.
Medications That Raise Blood Pressure
Common over-the-counter pain relievers, particularly ibuprofen and naproxen, can raise blood pressure by causing your kidneys to retain sodium and reduce blood flow. These drugs block an enzyme involved in pain signaling, but that same enzyme plays a role in kidney function. In people who are sensitive to salt, the resulting fluid retention is enough to measurably increase blood pressure. If you already take blood pressure medication, regular use of these painkillers can partially undo its effects.
Other medications known to raise blood pressure include decongestants containing pseudoephedrine, oral contraceptives, certain antidepressants, and stimulant medications. Excess alcohol, more than two drinks per day for men or one for women, also raises blood pressure through a combination of nervous system activation and hormonal effects.
Blood Pressure Categories to Know
The 2025 AHA/ACC guidelines define four categories based on the higher of your two numbers:
- Normal: below 120/80 mm Hg
- Elevated: 120 to 129 systolic with diastolic still below 80
- Stage 1 hypertension: 130 to 139 systolic or 80 to 89 diastolic
- Stage 2 hypertension: 140 or higher systolic, or 90 or higher diastolic
If your top and bottom numbers fall into different categories, the higher category applies. A reading of 138/76, for example, counts as Stage 1 hypertension even though the bottom number is normal. These thresholds matter because cardiovascular risk begins rising well before blood pressure reaches levels that cause symptoms.