Hypertension is the medical term for high blood pressure, defined in adults as a sustained reading of 130/80 mm Hg or higher. Those two numbers represent the force your blood exerts against artery walls: the top number (systolic) measures pressure when your heart beats, and the bottom number (diastolic) measures pressure between beats. When that force stays elevated over time, it damages blood vessels and strains the heart, increasing the risk of heart attack, stroke, and kidney disease.
Blood Pressure Categories in Adults
The American Heart Association and American College of Cardiology classify adult blood pressure into four categories:
- Normal: below 120/80 mm Hg
- Elevated: systolic 120 to 129 and diastolic below 80
- Stage 1 hypertension: systolic 130 to 139 or diastolic 80 to 89
- Stage 2 hypertension: systolic 140 or higher, or diastolic 90 or higher
If your systolic and diastolic numbers fall into two different categories, you’re classified at the higher one. So a reading of 138/72 counts as Stage 1 hypertension even though the diastolic number is normal. A single high reading doesn’t mean you have hypertension. The diagnosis requires consistently elevated readings taken on separate occasions.
What Happens Inside Your Arteries
Blood pressure is determined by two things: how much blood your heart pumps (cardiac output) and how much your blood vessels resist that flow (vascular resistance). Think of it like water through a garden hose. Turning up the faucet increases flow, while pinching the hose increases resistance. Either one raises the pressure inside.
In hypertension, the problem is usually increased vascular resistance. The small arteries that feed your capillary beds tighten up, narrowing the path blood has to travel. This constriction raises pressure throughout the system. Over months and years, that extra force thickens artery walls, makes them stiffer, and accelerates the buildup of fatty plaques. The heart, meanwhile, has to work harder to push blood through tighter vessels, and the muscle gradually thickens in response.
Primary vs. Secondary Hypertension
About 85 to 90 percent of adults with high blood pressure have primary (also called essential) hypertension. This type has no single identifiable cause. It develops gradually from a combination of genetics, aging, diet, body weight, physical activity level, and other lifestyle factors. Most people diagnosed with hypertension fall into this category.
The remaining 10 to 15 percent have secondary hypertension, meaning another medical condition is driving their blood pressure up. Hormonal imbalances are the largest contributor, responsible for 10 to 20 percent of secondary cases. The most common hormonal cause is a condition where the adrenal glands overproduce a hormone that tells the kidneys to retain salt and water, raising blood volume and pressure. Kidney disease accounts for roughly 2.5 to 6 percent of all hypertension cases, since damaged kidneys struggle to regulate fluid balance. Other triggers include narrowing of the artery that supplies the kidney, sleep apnea, thyroid disorders, and certain medications.
Secondary hypertension matters because treating the underlying condition can sometimes resolve or significantly improve the blood pressure problem. It’s worth investigating when high blood pressure appears suddenly, resists standard treatment, or develops in a young person with no family history.
How Blood Pressure Is Measured Correctly
A blood pressure reading is only as reliable as the conditions under which it’s taken. Small things can shift your numbers by 5 to 15 points, enough to push a borderline reading into a different category. The CDC recommends sitting in a comfortable chair with your back supported for at least five minutes before a reading. Your arm should rest on a table at chest height, and the cuff should sit on bare skin, not over a sleeve.
Crossing your legs, talking during the reading, or having a full bladder can all inflate the numbers. So can caffeine or exercise within the previous 30 minutes. For home monitoring, take two or three readings a minute apart and average them. Clinicians typically want readings from multiple visits before diagnosing hypertension, because “white coat” anxiety in a medical setting can temporarily raise blood pressure by itself.
How Hypertension Is Defined in Children
The definition of hypertension in children is more complex than in adults because normal blood pressure changes with age, sex, and height. For children ages 1 through 12, hypertension is defined as blood pressure at or above the 95th percentile for their age, sex, and height group. A child who is tall for their age naturally has slightly higher blood pressure than a shorter child of the same age, so the thresholds adjust accordingly. These percentile tables are based on data from normal-weight children.
Starting at age 13, the definitions shift to the same fixed numbers used for adults: 130/80 mm Hg or higher is Stage 1 hypertension, and 140/90 or higher is Stage 2. This alignment makes the transition from pediatric to adult care straightforward.
Hypertensive Crisis: When Numbers Spike Dangerously
A hypertensive crisis occurs when blood pressure spikes above 180/120 mm Hg. At this level, the distinction between urgent and emergency depends entirely on whether the pressure is actively damaging organs.
In a hypertensive urgency, the numbers are severely elevated but there’s no sign of organ damage. This still requires prompt medical attention, but the pressure can be lowered over hours to days. A hypertensive emergency, by contrast, means the extreme pressure is injuring the brain, heart, kidneys, or eyes in real time. Warning signs include severe headache, visual changes, confusion, chest pain, difficulty breathing, or decreased urine output. Damage to the retina, visible as tiny hemorrhages and swelling of the optic nerve, is a hallmark finding. This is a true medical emergency requiring immediate treatment.