High blood pressure happens when the force of blood pushing against your artery walls stays elevated over time. It develops through a combination of factors: how much fluid your body retains, how narrow or stiff your blood vessels become, and how hard your heart pumps. Normal blood pressure sits below 120/80 mm Hg, while Stage 1 hypertension starts at 130/80 and Stage 2 at 140/90.
Most cases have no single cause. Instead, several overlapping forces gradually push your numbers up.
How Your Body Controls Blood Pressure
Your kidneys, blood vessels, and hormones work together through a system that constantly adjusts blood pressure based on what your body needs. When pressure drops, your kidneys release an enzyme that triggers a chain reaction: your liver produces a protein that gets converted in your lungs and kidneys into a hormone that narrows the muscular walls of small arteries. That same hormone signals your adrenal glands to release another hormone that tells your kidneys to hold onto sodium. More sodium means more water stays in your bloodstream, which increases blood volume and pressure.
This system works well when it activates temporarily, like when you stand up quickly or lose fluid. Problems start when it stays overactive, keeping your vessels constricted and your fluid volume high even when they shouldn’t be. Genetics, diet, and other health conditions can all push this system into overdrive.
Sodium and Fluid Retention
Eating too much sodium raises blood pressure through two related pathways. The first is straightforward: extra sodium causes your body to retain water, increasing the total volume of blood your heart has to pump. The second is more direct and happens at the level of your blood vessel walls.
When sodium levels rise in your blood, sodium enters the cells lining your arteries through specialized channels. This makes those cells stiffer, and stiff lining cells can’t produce as much nitric oxide, a molecule that normally keeps blood vessels relaxed and flexible. Research published in the Proceedings of the National Academy of Sciences found that raising sodium concentration in these cells caused a 22% jump in cell stiffness. With less nitric oxide being released, the smooth muscle around your arteries tightens, increasing resistance to blood flow. So sodium doesn’t just add more fluid; it also makes your pipes narrower.
Aging and Artery Stiffness
Your arteries are built from a mix of elastic fibers and structural fibers. Elastic fibers let vessels stretch with each heartbeat and snap back, absorbing the pressure. Structural fibers provide strength but don’t stretch. As you age, elastic fibers break down and get replaced with stiffer structural material. Inflammatory damage and calcium deposits accelerate this process.
The result is arteries that can’t expand to cushion the surge of blood each time your heart beats. This specifically drives up the top number of your reading (systolic pressure) while the bottom number may stay the same or even drop, creating what’s called isolated systolic hypertension. It’s the most common form of high blood pressure in people over 60. Oxidative stress, essentially a buildup of damaging molecules in blood vessel cells, speeds up this stiffening by promoting inflammation and further structural changes in the vessel wall.
Stress Hormones and Your Nervous System
Short bursts of stress raise your blood pressure temporarily, which is normal. Chronic stress is a different story. When you’re under sustained pressure from work, finances, relationships, or other life circumstances, your body produces elevated levels of stress hormones including cortisol, norepinephrine, and epinephrine. These hormones increase heart rate, constrict blood vessels, and make your kidneys retain more fluid.
A large study tracked the relationship between stress hormone levels and cardiovascular outcomes over a median follow-up of 6.5 years. Each time stress hormone levels doubled, the risk of developing hypertension increased by 21% to 31%, depending on the specific hormone. This wasn’t a temporary spike; it reflected lasting changes in how the cardiovascular system operates under chronic hormonal exposure.
Physical Inactivity
Sitting for long periods raises blood pressure through a surprisingly active process. Prolonged inactivity elevates your sympathetic nervous system, the “fight or flight” branch that speeds up your heart and tightens blood vessels. One study in patients with type 2 diabetes found that extended sitting raised levels of noradrenaline (a key sympathetic hormone) by 11% to 18%, alongside blood pressure increases of about 10/5 mm Hg.
The mechanism goes beyond simple deconditioning. When you sit for hours, your metabolic demand drops and blood flow slows. Meanwhile, glucose and insulin levels rise after meals without the muscle activity that would normally clear them. Those elevated glucose and insulin levels further stimulate the sympathetic nervous system, creating a feedback loop that pushes blood pressure higher. Over months and years, this contributes to chronic vascular inflammation and reduced blood vessel flexibility.
Genetics and Family History
More than 100 genetic variations have been linked to essential hypertension, the type with no single identifiable medical cause. Many of these variations affect the kidney’s pressure-regulation system or the health of blood vessel lining cells. If your parents had high blood pressure, you carry a higher baseline risk regardless of lifestyle.
Genetics don’t work in isolation, though. Researchers also suspect that epigenetic changes play a role. These are modifications that affect how your genes behave without altering the DNA itself. Environmental exposures, diet, and stress can all trigger epigenetic shifts that influence blood pressure regulation. This helps explain why two people with similar genetic backgrounds can have very different blood pressure profiles depending on how they live.
Alcohol Consumption
Alcohol raises blood pressure in a dose-dependent way, meaning the more you drink, the higher the risk. A 2024 meta-analysis found an almost linear relationship: compared to light drinking (about one standard drink per day), consuming two drinks daily increased hypertension risk by 11%, three drinks by 22%, and four drinks by 33%. For women, the risk climbed significantly above roughly one drink per day. For men, risk increased steadily across all levels of intake.
One standard drink contains about 14 grams of alcohol, which is roughly a 12-ounce beer, 5 ounces of wine, or 1.5 ounces of liquor. The 12 grams per day threshold where risk begins to climb meaningfully is just under one standard drink.
Medications That Raise Blood Pressure
Several common over-the-counter and prescription medications can push your blood pressure up, sometimes without you realizing it.
- Pain relievers (NSAIDs): Ibuprofen and naproxen cause your body to retain water, which increases blood volume and puts extra load on the kidneys.
- Decongestants: Pseudoephedrine and phenylephrine, found in many cold and allergy medicines, work by narrowing blood vessels. That’s what reduces nasal swelling, but it also raises blood pressure body-wide.
- Hormonal birth control: Birth control pills and patches can raise blood pressure in some people. The risk increases if you’re over 35, overweight, or smoke.
If you take any of these regularly and your blood pressure has been creeping up, the medication itself could be a contributing factor.
Medical Conditions Behind Secondary Hypertension
About 5% to 10% of high blood pressure cases stem from a specific, identifiable medical condition. This is called secondary hypertension, and treating the underlying problem can sometimes resolve the blood pressure issue entirely. The most common causes, ranked roughly by frequency:
- Obstructive sleep apnea: Repeated drops in oxygen during sleep trigger surges in sympathetic nervous system activity that carry over into daytime blood pressure.
- Narrowed kidney arteries: Reduced blood flow to the kidneys tricks them into activating the pressure-raising hormone system as though your blood pressure is too low.
- Excess aldosterone production: The adrenal glands produce too much of the hormone that tells kidneys to retain sodium and water.
- Kidney disease: Damaged kidneys can’t filter sodium and fluid properly, leading to volume overload.
- Thyroid disorders: Both overactive and underactive thyroid function can raise blood pressure through different mechanisms.
- Adrenal tumors: Rare growths on the adrenal glands can produce excessive amounts of pressure-raising hormones.
Secondary hypertension is worth investigating if your blood pressure rises suddenly, doesn’t respond well to treatment, or develops before age 30. It’s also more likely if you have no family history of hypertension and no obvious lifestyle risk factors.