What causes high blood pressure? Primary and secondary hypertension explained

Short answer

What causes high blood pressure is usually a mix, not one trigger. In most adults it is primary hypertension: aging arteries, genes, salt, extra weight, alcohol, inactivity, poor sleep, and stress adding up over years. About 5–10% of cases are secondary, caused by a specific condition such as sleep apnea, kidney disease, or an adrenal hormone problem.

If your readings crept up even though you feel fine, you're not imagining it, and it's not your fault. High blood pressure is extremely common: under the US definition of 130/80 mm Hg or higher, it affects nearly half of all American adults, about 120 million people (doi.org). In a long-running Framingham study, 9 in 10 people who reached age 55 or 65 without hypertension went on to develop it later in life (doi.org). Blood pressure rising with age is the rule, not a personal failure. But it is still worth finding out why yours is rising, because several causes are fixable.

This article explains the difference between primary and secondary hypertension, the everyday habits that push pressure up, whether stress really causes high blood pressure, what makes it spike suddenly, why causes differ in young adults and in women, who should be checked for a hidden cause, and when a high reading is an emergency.

What causes high blood pressure: primary or secondary?

Doctors sort high blood pressure into two groups, and the split matters because it changes what you do next.

Primary hypertension (also called essential hypertension) is the common, gradual kind. There is no single cause. Instead, the systems that set your blood pressure — your arteries, kidneys, hormones, and nervous system — slowly drift toward a higher set point. Genes make some people more sensitive to that drift, and daily habits speed it up or slow it down.

Secondary hypertension means an identifiable condition or substance is pushing your pressure up. It accounts for roughly 5–10% of people with hypertension (doi.org). The most common causes include obstructive sleep apnea, primary aldosteronism (an adrenal gland making too much of the hormone aldosterone), kidney disease, narrowing of the arteries to the kidneys, and some medicines. These matter because treating the cause can lower blood pressure, sometimes a lot. Even so, pressure often doesn't return fully to normal after the cause is treated, which is one more reason to find it early (doi.org).

Here's the picture at a glance:

The line between the two groups is blurrier than it looks. In a US study that tested 1,015 people for primary aldosteronism no matter what their hormone levels looked like, the condition turned up in 11.3% of people with normal blood pressure, 15.7% with stage 1 hypertension, 21.6% with stage 2, and 22.0% with resistant hypertension (high pressure that stays high despite three or more medicines) (doi.org). The authors concluded that some of what we call "essential" hypertension may actually be hormone-driven. If you want a refresher on the numbers themselves, see what blood pressure numbers mean.

What causes primary hypertension?

Primary hypertension builds from several causes stacked on top of each other. No one of them is the whole story, but each adds a few points.

Age and stiffer arteries

Healthy arteries stretch with every heartbeat and spring back. With age they slowly stiffen, so the same heartbeat produces a higher pressure. That's why the lifetime risk is so high: in the Framingham Heart Study, the remaining lifetime risk of developing hypertension (defined there as 140/90 mm Hg or higher) was 90% for people who were free of it at 55 or 65 (doi.org).

Genes and family history

Blood pressure runs in families. A genetic study of more than 1 million people found 535 new places in the genome linked to blood pressure, adding to hundreds already known (doi.org). Each gene variant has a tiny effect on its own. Together they shape how sensitive your body is to salt, weight gain, and stress. Your genes load the dice, but they don't decide the result.

Salt and sodium

Sodium makes your body hold on to water and changes how tightly your blood vessels squeeze. The effect is bigger than many people think. In a 2023 crossover trial, 213 adults aged 50 to 75 spent one week on a high-sodium diet and one week on a low-sodium diet (about 500 mg of sodium a day). Median systolic pressure — the top number — was 126 mm Hg on the high-sodium week and 119 mm Hg on the low-sodium week. Blood pressure fell in 73.4% of people, whether or not they had hypertension or took blood pressure medicine (doi.org).

People also differ. In the same trial, 46% of participants met the usual definition of "salt sensitive," with a drop of 5 mm Hg or more in their average pressure on the low-sodium diet (doi.org).

Cutting salt doesn't just move numbers. In the Salt Substitute and Stroke Study, 20,995 older adults in 600 villages in rural China who had had a stroke or were 60 or older with high blood pressure were given either regular salt or a salt substitute made of 75% sodium chloride and 25% potassium chloride. Over about 4.7 years, the salt-substitute group had fewer strokes: 29.14 vs. 33.65 per 1,000 person-years, a 14% lower rate (doi.org). If you have kidney disease or take medicines that raise potassium, ask your doctor before trying a potassium-based salt substitute.

The 2025 AHA/ACC guideline recommends keeping sodium below 2,300 mg a day, ideally moving toward 1,500 mg (doi.org).

Extra weight, especially around the middle

Extra body weight raises blood pressure through several paths at once: more blood volume, more work for the heart, higher insulin levels, and a more active "fight-or-flight" nervous system. It also raises the risk of sleep apnea, which adds its own push. The good news is that the effect runs both ways. In a meta-analysis of 25 randomized trials with 4,874 people, losing about 5.1 kg lowered blood pressure by about 4.4/3.6 mm Hg — roughly 1 mm Hg for every kilogram lost (doi.org). Fat stored deep in the belly matters most; we explain why in visceral fat after 35.

Alcohol

Alcohol raises blood pressure in a dose-dependent way. In a meta-analysis of 36 trials with 2,865 people, cutting back lowered blood pressure in those who drank more than two drinks a day. People who drank six or more drinks a day and cut their intake by about half saw systolic pressure fall by about 5.5 mm Hg and diastolic by about 4 mm Hg (doi.org). The 2025 guideline says not drinking is best; for adults who do drink, it advises no more than one drink a day for women and two for men (doi.org). Alcohol also disrupts sleep and heart rhythm overnight, which you can often see the next morning; read more in how alcohol affects next-day HRV, heart rate, and sleep.

Too little movement

Regular movement keeps blood vessels flexible and calms the nervous system at rest. In a network meta-analysis of 270 randomized trials with 15,827 people, aerobic exercise training lowered resting blood pressure by about 4.5/2.5 mm Hg, and isometric exercise — holding a position, like a wall sit or a handgrip squeeze — produced the largest drops of all the exercise types studied (doi.org). For a full plan built on these habits, see how to lower high blood pressure.

Short or poor sleep

Blood pressure is supposed to dip at night. When sleep is short or broken, that dip gets smaller and the nervous system stays switched on. In a meta-analysis of 16 cohort studies following 1,044,035 people, short sleep was linked to a 7% higher risk of developing hypertension, rising to 11% for people sleeping under five hours (doi.org). Sleeping longer than usual was not linked to higher risk. These are observational studies, so they show a link, not proof that short sleep causes hypertension.

Can stress cause high blood pressure?

Yes in the short term, and probably in the long term too — but the long-term evidence is weaker than most people assume.

Short-term stress raises blood pressure for sure. When you're stressed, your body releases adrenaline and cortisol, your heart beats faster and harder, and your blood vessels tighten. A tense meeting, a near-miss in traffic, or a sharp pain can all push a reading up within minutes. That response is normal and fades once the stress passes.

Chronic stress is linked to hypertension, with caveats. A meta-analysis of 11 studies with 5,696 people found that chronic psychosocial stress was linked to about 2.4 times higher odds of hypertension (doi.org). The authors were careful: the studies measured stress in very different ways, and more research is needed to confirm the link. "Stress" in these studies covers work strain, money worries, caregiving, and poor sleep, which are hard to separate from each other.

Stress often works through habits. Stress can push up blood pressure indirectly, through shorter sleep, more drinking, less exercise, comfort eating, and weight gain around the belly. That's why stress management tends to help most when it improves those habits too. We look at this chain in stress and weight gain.

What does this mean for you? Stress is a real piece of the puzzle, but it rarely explains hypertension on its own. If your readings are high, "I've just been stressed" is a reason to look closer, not a reason to skip follow-up.

What causes high blood pressure to spike suddenly?

A sudden jump in your reading is usually caused by something short-lived. The common culprits:

• Caffeine. In people with hypertension, 200–300 mg of caffeine (about two cups of coffee) raised blood pressure by about 8/6 mm Hg on average. The rise started within an hour and lasted at least three hours. Over two weeks, though, regular coffee drinking didn't raise blood pressure (doi.org). It makes sense to skip coffee right before you measure.

• Pain-relief pills (NSAIDs). Ibuprofen, naproxen, and similar drugs can nudge pressure up over weeks. In a randomized trial of 444 people with arthritis, four months of ibuprofen raised 24-hour systolic pressure by 3.7 mm Hg. Among people who started with normal pressure, 23.2% on ibuprofen and 19.0% on naproxen developed hypertension, compared with 10.3% on celecoxib (doi.org).

• Decongestants. Across 24 trials with 1,285 people, pseudoephedrine raised systolic pressure by about 1 mm Hg on average and heart rate by about 3 beats per minute; higher doses and immediate-release forms had bigger effects (doi.org). The average is small, but some people react more.

• Pain, anger, and anxiety. Anything that triggers the fight-or-flight response can push a reading up in the moment.

• The doctor's office. Among people whose office readings are in the hypertensive range, 15–30% have normal readings outside the office. This is called white-coat hypertension (doi.org).

• How you measure. Sitting without back support can add 5–15 mm Hg to the top number, crossing your legs can add 5–8 mm Hg, and a cuff that's too small gives falsely high readings (doi.org). Our guide to blood pressure monitors at home walks through proper technique.

• Missed medication doses. Skipping blood pressure medicine can let readings rebound. Never stop a medicine on your own.

Other things can move readings too, including the weather; if your numbers shift during hot spells, see how summer heat affects blood pressure.

The practical rule: one high reading is not a diagnosis. Sit quietly for five minutes, back supported and feet flat, and measure again. If readings stay high over several days, that's a pattern worth showing your doctor. If a reading is higher than 180/120 mm Hg, follow the steps in the next section.

Hypertensive crisis: when should you call 911?

A reading higher than 180/120 mm Hg is a hypertensive crisis level. What you do next depends on whether you have symptoms.

The 2025 AHA/ACC guideline now calls a reading above 180 systolic and/or 120 diastolic severe hypertension when there is no sign of sudden organ damage; it replaced the older term "hypertensive urgency." When the same numbers come with new or worsening damage to organs such as the brain, heart, kidneys, eyes, or the aorta, it is a hypertensive emergency (doi.org).

The American Heart Association gives these steps for home readings (heart.org):

1. Wait at least one minute and measure again.

2. If it's still higher than 180/120 and you have no symptoms, you likely have severe hypertension. This usually doesn't need a hospital stay, but contact your healthcare professional as soon as possible.

3. If it's higher than 180/120 and you have any of these symptoms, call 911: chest pain, shortness of breath, back pain, numbness, weakness, change in vision, or difficulty speaking.

Don't wait to see if symptoms pass, and don't drive yourself if you feel unwell. Don't take extra doses of your blood pressure medicine unless a doctor has told you to.

What are the causes of secondary hypertension?

Secondary hypertension has a findable cause. These are the most common ones.

Obstructive sleep apnea

In sleep apnea, the airway repeatedly closes during sleep. Each pause drops oxygen and jolts the nervous system awake, pushing blood pressure up at night and, over time, during the day. In the Wisconsin Sleep Cohort, 709 adults had overnight sleep studies. People with 15 or more breathing pauses per hour had 2.89 times higher odds of hypertension four years later than people with none, even after accounting for weight (doi.org). Among 125 people with resistant hypertension who were checked for every known cause, sleep apnea was found in 64.0% — far more than any other cause (doi.org). Loud snoring, gasping at night, and daytime sleepiness are clues; see could I have sleep apnea? and sleep apnea treatment options.

Primary aldosteronism

Aldosterone tells your kidneys to hold on to salt and water. When one or both adrenal glands make too much of it, blood pressure rises and potassium can fall. As noted above, it's far more common than once thought: up to about 1 in 5 people with stage 2 or resistant hypertension (doi.org). It's also more dangerous than primary hypertension at the same blood pressure. In a meta-analysis of 31 studies, people with primary aldosteronism had 2.58 times the odds of stroke and 3.52 times the odds of atrial fibrillation (an irregular heart rhythm) compared with people with primary hypertension (doi.org).

Yet it's rarely tested. Among 269,010 US veterans with treatment-resistant hypertension, only 1.6% were ever tested for primary aldosteronism (doi.org). The test is a simple blood draw measuring aldosterone and renin.

Kidney disease and narrowed kidney arteries

Your kidneys set your body's salt and fluid balance. Chronic kidney disease disrupts that control. Narrowing of the arteries that feed the kidneys (renovascular disease) makes the kidneys "think" pressure is too low, so they release hormones that raise it (doi.org).

Thyroid and other hormone disorders

Thyroid problems, Cushing syndrome (too much cortisol), and pheochromocytoma (a rare tumor that releases adrenaline-like hormones) are less common causes that doctors check for when the story fits (doi.org). Pheochromocytoma can cause bursts of pounding heartbeat, headache, and sweating. If you have signs of a thyroid problem, see signs of thyroid problems in women.

Medicines and substances

NSAIDs and decongestants are covered above. Birth control pills can also raise blood pressure (more on that below), and guidelines include a review of medicines and other substances that raise blood pressure as part of the workup for a secondary cause (doi.org). Don't stop any prescribed medicine on your own; ask your doctor whether it could be playing a role.

Who should be screened for secondary hypertension?

Doctors look harder for a secondary cause when something about your blood pressure doesn't fit the usual pattern:

• it started young, especially before 40;

• it's severe, came on suddenly, or got much worse after being stable;

• it stays high despite three or more medicines (resistant hypertension);

• your potassium is low, or you have sleep apnea, an adrenal mass found on a scan, or a family history of early hypertension or stroke.

The 2025 AHA/ACC guideline recommends screening for primary aldosteronism in adults with hypertension plus any of the following: resistant hypertension, low potassium, obstructive sleep apnea, an incidental adrenal mass, or a family history of early-onset hypertension or stroke before age 40. It says screening may also be considered in everyone with stage 2 hypertension (doi.org). The Endocrine Society's 2025 guideline goes further and suggests screening all people with hypertension (doi.org).

What causes high blood pressure in young adults?

High blood pressure isn't only an older person's problem. In US national survey data from 2013–2014, 7.3% of adults aged 18 to 39 had hypertension. Young adults were also the least likely to know it: 74.7% were aware, 50.0% were treated, and 40.2% had it under control, lower than in middle-aged and older adults (doi.org). Young men fared worst, partly because they see doctors less often.

In young adults, the everyday drivers are the same as in older people — weight, salt, alcohol, inactivity, short sleep, and family history. But a hidden cause is more likely than many people assume. In a study of 2,090 adults aged 18 to 40 with confirmed hypertension who had a full workup for secondary causes, 29.6% had one (doi.org). Among those with a secondary cause:

• 54.8% had primary aldosteronism;

• 18.4% had renovascular hypertension (narrowed kidney arteries);

• 12.9% had primary kidney disease;

• 5.9% had a pheochromocytoma or related tumor;

• 6.0% had hypertension caused by drugs or substances.

The authors concluded that everyone diagnosed with hypertension before age 40 should be screened for secondary causes (doi.org). If you're in your 20s or 30s and your readings are high, it's reasonable to ask your doctor, "Should we check for a secondary cause?"

Also think about what you take: decongestants, NSAIDs, stimulant medicines, and heavy caffeine or energy drink use can all push readings up in younger people too.

What causes high blood pressure in women?

Women share all the causes above, plus a few that are specific to hormones and life stages.

Blood pressure rises faster in women than many realize. In an analysis of 32,833 people followed across four US community studies, women's blood pressure climbed more steeply than men's, starting as early as the third decade of life and continuing through the life course (doi.org). The old idea that women "catch up" to men only after menopause doesn't hold.

Birth control pills. In a study of 68,297 US nurses aged 25 to 42, current users of oral contraceptives had 1.8 times the risk of developing hypertension compared with women who had never used them. The absolute risk was small — about 41.5 extra cases per 10,000 women per year — and risk dropped quickly after stopping (doi.org). If you take the pill, a yearly blood pressure check is a good habit. If your readings rise, ask about non-estrogen methods.

Pregnancy and preeclampsia. Preeclampsia — high blood pressure in pregnancy with signs of organ strain — affects about 2–8% of pregnancies worldwide (doi.org). It usually resolves after birth, but it leaves a mark: women who had preeclampsia had 3.7 times the risk of developing hypertension about 14 years later (doi.org). If you had preeclampsia or high blood pressure in pregnancy, tell every doctor you see, and keep checking your blood pressure for years afterward. If you are pregnant or recently gave birth and have a severe headache, vision changes, or a very high reading, contact your care team right away.

Menopause. In the SWAN study of 3,302 midlife women, about a third followed a systolic blood pressure path that sped up about a year after their final period, a pattern pointing to menopause itself and not just age. Women with hot flashes and night sweats tended to have higher blood pressure over time (doi.org). The authors recommend checking blood pressure often during the menopause transition.

Thyroid problems and sleep apnea are also worth considering; both are underdiagnosed in women.

What Welltory data shows about blood pressure and wearables

Welltory doesn't measure blood pressure, but we can compare wearable patterns in people who report high blood pressure with those who don't. Among 815 users who self-report high blood pressure and 957 who self-report normal readings, no single wearable number cleanly separated the two groups. Resting heart rate, overnight recovery, and HRV scores overlapped almost entirely: about 83% overlap on the morning HRV score, and 46% of the high blood pressure group sat inside the normal group's middle range.

The differences that did appear were about behavior, and they were modest. The high blood pressure group was less active: 58.5% averaged under 7,000 steps a day, compared with 48.4% of the normal group. They also recovered slightly worse overnight: 40.5% had a low morning "battery" score, compared with 30.0%. And they carried a higher stress load by the end of the day. These gaps are small (Cohen's d about 0.2 to 0.25, a small effect size) and held up after accounting for how many other health conditions people reported.

Two takeaways. First, your watch can't tell you your blood pressure — you still need a cuff. Second, the gaps line up with the modifiable habits above: movement, recovery, and stress. That's a reason to track patterns over time, not a single number.

When to see a doctor about high blood pressure

High blood pressure usually doesn't announce itself. You can feel perfectly well while your readings strain your heart, brain, kidneys, and blood vessels. See a doctor if:

• your home readings are repeatedly 130/80 mm Hg or higher (the US threshold) (doi.org); European guidelines use 140/90 mm Hg (doi.org);

• your pressure rose suddenly, or you're under 40 with high readings;

• it stays high despite medication;

• you have low potassium, loud snoring or pauses in breathing at night, or episodes of pounding heart, headache, and sweating;

• you had preeclampsia or high blood pressure in a past pregnancy;

• a new medicine, birth control pill, or supplement seems to have pushed your numbers up.

Get emergency care for a reading higher than 180/120 mm Hg with chest pain, shortness of breath, back pain, numbness, weakness, vision changes, or trouble speaking (heart.org).

How to bring this up with your doctor — and what to ask for

Say it plainly. "My home readings have been around 145/92 for the last month, and I'd like to understand why" is clear and useful. Give real numbers rather than "it's a bit high."

Bring context. A week or two of home readings, taken the same way at the same times, is far more useful than one office number. Note what else was going on: poor sleep, a stressful stretch, a new medicine, pain pills, cold medicine, heavy drinking, or a new birth control method. Our guide to keeping a blood pressure log for your doctor shows what to record.

Ask these specifically. Could this be white-coat hypertension — should we confirm with home or 24-hour monitoring? Could any of my medicines or supplements be raising it? Should I be checked for primary aldosteronism with an aldosterone and renin test? Could I have sleep apnea — should I have a sleep study? Should we check my kidney function, potassium, and thyroid? If you're under 40: should we look for a secondary cause?

If you are dismissed. "I understand it may just be primary hypertension, but guidelines suggest checking for secondary causes in my situation. Can we note my readings in my record and discuss testing?" A written record makes follow-up more likely.

How Welltory helps

Welltory doesn't measure blood pressure, and no wearable can replace a validated cuff. What it does measure are many of the everyday drivers behind your readings: your sleep, your stress load across the day, your heart rate variability (HRV) and resting heart rate, your steps, and your morning energy — each compared with your own baseline.

That lets you see the patterns that doctors ask about. Do your worst weeks line up with short nights, a run of high-stress days, or a drop in activity? Does a night of drinking show up as a poor recovery score the next morning? With My Patterns, you can add notes like "BP 148/94," "cold medicine," "late coffee," or "poor sleep," and over a few weeks see what tends to come before your higher readings. It won't diagnose hypertension or find a secondary cause, but it turns a vague sense that "my blood pressure has been high lately" into a timeline you can bring to your doctor.

How we made it

The clinical content rests on published guidelines and research: the 2025 AHA/ACC high blood pressure guideline (Jones et al. 2025) and its case-based applications (Cameron et al. 2025), the 2023 ESH guidelines (Mancia et al. 2023), the Endocrine Society guideline on primary aldosteronism (Adler et al. 2025), the AHA statement on blood pressure measurement (Muntner et al. 2019) and AHA public guidance on hypertensive crisis; lifetime risk and genetics (Vasan et al. 2002; Evangelou et al. 2018); secondary hypertension reviews and studies (Rimoldi et al. 2014; Brown et al. 2020; Monticone et al. 2018; Cohen et al. 2021; Pedrosa et al. 2011; de Freminville et al. 2024); randomized trials and meta-analyses of sodium (Gupta et al. 2023; Neal et al. 2021), weight loss (Neter et al. 2003), alcohol (Roerecke et al. 2017), exercise (Edwards et al. 2023), caffeine (Mesas et al. 2011), NSAIDs (Ruschitzka et al. 2017) and decongestants (Salerno et al. 2005); cohort data on sleep apnea (Peppard et al. 2000), sleep duration (Hosseini et al. 2024), stress (Liu et al. 2017), young adults (Zhang & Moran 2017), and women (Ji et al. 2020; Chasan-Taber et al. 1996; Bellamy et al. 2007; ACOG 2020; Samargandy et al. 2022).

The Welltory figures come from an anonymized, aggregated comparison of 815 users who self-report high blood pressure and 957 who self-report normal blood pressure, filtered to users with good wearable-data quality. Wearable summaries included activity, resting heart rate, HRV score, morning recovery, and stress load. Differences were small (Cohen's d ≈ 0.2–0.25) and persisted across strata by number of reported conditions. Self-report is a selector, not a diagnosis, and no mm Hg values are part of the dataset.

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