High blood pressure rarely has a single cause. In most cases, it develops from a combination of factors: your genetics, what you eat, how much you move, how well you sleep, and how your body changes with age. About 30% to 60% of your blood pressure variation is inherited, which means the rest comes down to lifestyle, environment, and sometimes an underlying medical condition you may not know about.
How Blood Pressure Categories Work
Before digging into causes, it helps to know where you stand. The 2025 guidelines from the American Heart Association and American College of Cardiology define four categories for adults:
- Normal: below 120/80
- Elevated: 120 to 129 systolic (top number) with the bottom number still under 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, you’re classified by the higher one. Many people discover they’ve crossed into Stage 1 without any symptoms at all.
The Role of Salt and Fluid Balance
Sodium is one of the best-understood drivers of high blood pressure. When you eat more salt than your kidneys can efficiently clear, your body holds onto extra water to dilute it. That extra fluid increases the volume of blood flowing through your arteries, raising pressure against the vessel walls.
But the damage goes beyond fluid retention. High sodium intake also stiffens blood vessels, impairs the lining of your arteries, and ramps up activity in the nervous system pathways that constrict blood vessels. Over time, the constant pressure load remodels the walls of smaller arteries, making them thicker and narrower, which locks in higher resistance even if you later cut back on salt.
Potassium works as a natural counterbalance. Clinical trials consistently show that the ratio of sodium to potassium in your diet is more strongly linked to blood pressure than either mineral alone. Most people eat far more sodium and far less potassium than their bodies are designed for. Increasing potassium-rich foods (bananas, potatoes, beans, leafy greens) while reducing processed food is one of the most effective dietary shifts you can make.
Your Hormonal Pressure Control System
Your body has a built-in system for fine-tuning blood pressure called the renin-angiotensin-aldosterone system, or RAAS. When your kidneys sense low blood flow or low salt delivery, they release an enzyme that triggers a cascade ending with a powerful hormone called angiotensin II. This hormone constricts blood vessels, tells your adrenal glands to release aldosterone (which makes your kidneys reabsorb more sodium and water), and increases nervous system signals that further tighten arteries.
In a healthy body, this system turns on when pressure drops and turns off when it recovers. In hypertension, the system can become chronically overactive, keeping vessels constricted and fluid volume high even when neither response is needed. This overactivation also promotes inflammation, stiffening, and scarring in blood vessel walls and the heart. Most common blood pressure medications work by interrupting one or more steps in this cascade.
How Aging Changes Your Arteries
Even people who eat well and exercise regularly tend to see blood pressure creep up with age. The main reason is structural: the walls of your largest arteries, especially the aorta, gradually lose their elastic fibers and replace them with stiffer collagen. Young, flexible arteries stretch when the heart pumps and then gently recoil, smoothing out the pressure wave. Stiff arteries can’t do this, so the peak pressure from each heartbeat hits harder.
This is why isolated systolic hypertension (a high top number with a normal bottom number) is so common after age 60. The process is accelerated by smoking, high blood sugar, and chronic inflammation, but some degree of stiffening happens in nearly everyone.
Genetics and Family History
If one or both of your parents had high blood pressure, your risk is substantially higher. Studies of twins and families estimate that 30% to 60% of blood pressure variation comes from inherited factors. There’s no single “hypertension gene.” Instead, hundreds of small genetic variations each nudge your blood pressure slightly higher by affecting how your kidneys handle salt, how your blood vessels respond to hormonal signals, or how sensitive your nervous system is to stress.
Ethnic background matters too. People of African descent, for example, tend to develop hypertension earlier and at higher rates, partly due to genetic differences in salt sensitivity and vascular function. These genetic factors don’t guarantee high blood pressure, but they lower the threshold at which lifestyle factors like sodium, weight, or inactivity push you over the line.
Insulin Resistance and Metabolic Syndrome
Carrying extra weight, especially around the midsection, often goes hand in hand with insulin resistance, a condition where your cells stop responding normally to insulin. When this happens, your body produces more and more insulin to compensate, and chronically elevated insulin directly raises blood pressure in several ways.
First, insulin tells the kidneys to hold onto sodium, pulling water along with it. This effect is preserved (and even amplified) in people who are insulin resistant, so you retain more fluid even as the rest of your metabolism struggles. Second, insulin resistance causes the loss of insulin’s normal ability to relax blood vessels while amplifying the constriction caused by circulating fatty acids and oxidative stress. Third, high insulin levels can upregulate the same angiotensin receptors that tighten blood vessels and expand blood volume. These overlapping mechanisms explain why hypertension, abdominal obesity, high blood sugar, and abnormal cholesterol so frequently cluster together in what’s called metabolic syndrome.
Sleep Apnea: A Hidden Driver
Obstructive sleep apnea is the most common secondary cause of high blood pressure, and it’s dramatically underdiagnosed. During sleep, the airway repeatedly collapses, cutting off oxygen for seconds to over a minute at a time. Each episode triggers a spike in stress hormones and activates the “fight or flight” branch of the nervous system, constricting blood vessels and raising heart rate.
What makes sleep apnea especially damaging is that these surges don’t stay confined to nighttime. The elevated stress hormone levels and heightened nervous system activity carry over into waking hours, driving blood pressure up around the clock. The repeated drops in oxygen also trigger chronic inflammation and oxidative stress that injure blood vessel walls. If your blood pressure is hard to control despite medication, or if you snore heavily and wake up feeling unrefreshed, sleep apnea is worth investigating. Treating it often brings meaningful blood pressure improvement.
Medications and Substances That Raise Blood Pressure
Several common medications can quietly push your blood pressure higher. Anti-inflammatory pain relievers like ibuprofen and naproxen are among the most frequent culprits. They cause the kidneys to retain sodium and fluid by blocking the same enzymes that help regulate blood flow to the kidneys. If you take these regularly for joint pain or headaches, they may be undermining your blood pressure control.
Other medications linked to blood pressure increases include:
- Decongestants (pseudoephedrine and phenylephrine, found in many cold and sinus products)
- Oral contraceptives
- Some antidepressants
- Corticosteroids prescribed for inflammation or autoimmune conditions
- Certain antipsychotic medications
Alcohol, nicotine, and recreational stimulants also raise blood pressure. Heavy alcohol use is particularly insidious because its effect builds gradually and can make prescribed blood pressure medications less effective. If you’ve noticed a loss of control in previously stable blood pressure, reviewing everything you take, including over-the-counter products and supplements, is a practical first step.
Putting the Pieces Together
For most people, high blood pressure isn’t caused by one thing going wrong. It’s the accumulation of several moderate risk factors: a genetic predisposition, a diet heavier on processed food than vegetables, a few extra pounds around the middle, less physical activity than the body needs, and arteries that are gradually stiffening with age. Each factor raises the baseline a little, and together they push past the threshold. The flip side is encouraging: because multiple factors contribute, improving even one or two of them, like reducing sodium, increasing potassium, losing a modest amount of weight, or treating sleep apnea, can produce a meaningful drop in blood pressure, sometimes enough to change your category entirely.