High Blood Pressure Explained: Numbers, Risks and Management

Blood pressure is the force of blood pushing against the walls of your arteries as the heart pumps it around the body. It is written as two numbers, for example 120/80, and measured in millimetres of mercury (mmHg). If you want the background on how the heart generates that force, see how the heart works.

The World Health Organization (WHO) explains that the first number, the systolic pressure, is the pressure in the blood vessels when the heart contracts or beats. The second number, the diastolic pressure, is the pressure in the vessels when the heart rests between beats. The top number is always the higher one.

WHO defines hypertension as pressure in the blood vessels that is too high, at 140/90 mmHg or higher. It says a diagnosis requires readings at or above 140 systolic and/or 90 diastolic on two different days. The NHS in the United Kingdom uses the same clinic threshold of 140/90, and describes home readings of 135/85 or higher as usually considered high.

Other bodies draw the lines differently. The US National Heart, Lung, and Blood Institute (NHLBI) describes consistent readings of 130 systolic or higher, or 80 diastolic or higher, as high, and lists a stage 2 band starting at 140 or 90. Thresholds differ between countries and guidelines, which is one reason a clinician, not an internet page, should interpret any individual reading.

WHO states that most people with hypertension do not feel any symptoms, and that the only way to know is to have your blood pressure checked. Very high readings can cause headaches, blurred vision and chest pain, but these are not a reliable early warning.

The numbers behind the silence are striking. WHO estimates that 1.4 billion adults aged 30 to 79 had hypertension in 2024, about 33% of that age group. Of those, roughly 600 million (44%) are unaware they have it, about 630 million (44%) are diagnosed and treated, and about 320 million (23%) have it under control. WHO also reports that two-thirds of adults with hypertension live in low- and middle-income countries. The fact sheet gives regional prevalence only for the Eastern Mediterranean and Western Pacific regions, so this page does not quote a figure for any other region.

Pressure that stays high strains the arteries, heart, brain and kidneys. WHO says untreated hypertension can harden arteries and reduce blood flow to the heart, which can lead to chest pain (angina), heart attack, heart failure and an irregular heartbeat. It can also burst or block arteries supplying the brain, causing a stroke, and can damage the kidneys, leading to kidney failure. The NHS lists heart disease, heart attacks, strokes, heart failure and kidney disease among the risks, and notes that even a small reduction in blood pressure lowers them.

For more on two of these outcomes, see heart failure basics and stroke signs and what to do.

WHO lists older age, genetics, being overweight or obese, physical inactivity, a high-salt diet and drinking too much alcohol among the things that raise risk. It also names tobacco use, a diet high in saturated and trans fats, low intake of fruit and vegetables, and air pollution. Among factors that cannot be changed, it lists family history, age over 65 and coexisting diseases such as diabetes or kidney disease.

The NHS adds a family history, long periods of stress and smoking. It also says people with a Black African, Black Caribbean or South Asian ethnic background are at higher risk, a statement made in a UK context. Diet is one lever that many people can influence, and salt and heart health looks at it in more detail.

Management usually combines lifestyle measures with medicine where a clinician judges it necessary. WHO lists a healthy low-salt diet, weight loss, physical activity and quitting tobacco, and says that if you have high blood pressure your doctor may recommend one or more medicines. The NHS says a doctor may prescribe medicine if pressure is very high, if the person has a higher risk of heart attack or stroke, or if pressure stays high despite lifestyle changes. Most are once-daily tablets, and some people need more than one.

WHO gives a general goal of below 140/90 for most people and below 130/80 for people with cardiovascular disease, diabetes, chronic kidney disease or high cardiovascular risk. Targets are individual, so they are set by a clinician. Checking at home between visits is one way to track progress; see measuring blood pressure at home.

Anyone who has never had their blood pressure checked, or has not had it checked for some time, can ask a clinic or pharmacy to do so. The NHS advises calling its urgent line for frequent headaches, blurred vision or chest pain that comes and goes. Sudden chest pain or pressure that does not go away, or pain spreading to the arms, neck, jaw or back, needs emergency care. Emergency numbers differ by country, so use your local emergency number. Do not start or stop any medicine without a clinician's advice.

Hypertension means pressure in the arteries that stays too high, and it usually gives no warning. Only a measurement can detect it, and a clinician confirms the diagnosis. Left uncontrolled it raises the risk of heart attack, stroke, heart failure and kidney damage, and it is managed with lifestyle change and, for many people, prescribed medicine.