What is high blood pressure?

High blood pressure is often called “the silent killer” — a phrase that isn't exaggerated at all, given how this extremely common condition can progress for years without causing any noticeable symptom, before sometimes suddenly showing up as a serious complication.

Pressure that's too strong on the artery walls

Hypertension is blood pressure against the artery walls that is persistently too high. This pressure is expressed as two numbers: systolic pressure (when the heart contracts to eject blood into the arteries) and diastolic pressure (between beats, when the heart relaxes and fills with blood again). Applied continuously over several years, this excess pressure gradually weakens the arteries — by thickening and stiffening their walls — as well as the heart itself, which has to work harder to push blood against this increased resistance.

An extremely common condition, everywhere in the world

In France, about 17 million adults live with high blood pressure, nearly a third of the adult population — and among them, one in four still receives no treatment. In the United States, measured prevalence is even higher: nearly 48% of adults are affected (CDC data, 2021-2023) — a gap largely explained by a lower diagnostic threshold used in the United States, a question covered in detail in the next article on this blog. Worldwide, the World Health Organization estimates that about 1.4 billion adults aged 30 to 79 lived with hypertension in 2024, about a third of that age group globally — a figure that has nearly doubled over the past thirty years, largely due to global population aging and changing lifestyles.

The problem of underdiagnosis

What makes hypertension particularly concerning at a population level is the proportion of people who don't know they have it. According to the WHO, about 44% of adults with hypertension worldwide don't know they have it. In the United States, that figure reaches about 41%. With no symptom to raise a flag, only regular blood pressure measurement can detect it — which is exactly the value of a home blood pressure monitoring protocol, rather than waiting for a sign that, most of the time, won't appear until a complication occurs.

Why hypertension so often stays silent

Contrary to what you might imagine, very high blood pressure generally causes no particular sensation in most people affected — the body gradually adapts to this increased pressure, without triggering a clear warning sign. When symptoms do appear (headaches, ringing in the ears, dizziness), they generally occur at already very high pressure levels, or during sudden swings — which doesn't reflect the situation of the vast majority of people with hypertension, whose blood pressure stays elevated in a stable, silent way.

Essential and secondary hypertension: an important distinction

So-called essential (or primary) hypertension, which accounts for about 95% of cases in adults, has no single identifiable cause — it results from a complex interaction between genetic predisposition and lifestyle factors. This is the most common form of hypertension, and the one this tool and this entire blog are about.

A minority of cases (about 5% in adults, but more than 95% in children and teenagers) are so-called secondary hypertension, linked to a specific identifiable cause — among the main ones:

• Kidney disease (chronic kidney failure, renal artery stenosis)
• Hormonal disorders (primary hyperaldosteronism, pheochromocytoma, Cushing's syndrome, thyroid disorders)
• Certain medications (non-steroidal anti-inflammatory drugs, corticosteroids, some oral contraceptives, nasal decongestants)
• Sleep apnea, itself detectable through another tool available on Hygietest
• A rare congenital abnormality (coarctation of the aorta)

This distinction isn't purely academic: secondary hypertension requires treating the underlying cause in addition to, or sometimes instead of, standard antihypertensive treatment — a point beyond the scope of this screening tool, but one that explains why certain warning signs (very severe hypertension from the start, sudden onset, hypertension resistant to several treatments) lead a doctor to look for a secondary cause rather than settle for a diagnosis of essential hypertension alone.

Why regular screening matters so much

Unlike other cardiovascular risk factors, hypertension isn't something the vast majority of people affected can “feel” day to day. This is why regular measurement — using a home blood pressure monitor following a rigorous protocol — remains the only reliable way to know where you stand, independent of any physical sensation. This lack of felt symptoms also explains why so many people with hypertension remain untreated: with no symptom to alert them or prompt regular check-ups, diagnosis can be delayed by several years.

How to measure your blood pressure correctly at home

A measurement is only valuable if taken under the right conditions. The French National Authority for Health (HAS) and the French Society of Hypertension recommend the “rule of 3”: three measurements in the morning before breakfast and any medication, three measurements in the evening before bed, one to two minutes apart, for three days in a row. You then average the eighteen readings. An average of 135/85 mmHg or higher suggests hypertension, to be confirmed with a doctor.

A few precautions make the result reliable:

• use a validated automatic monitor, preferably an upper-arm cuff rather than a wrist one, in the correct size;
• sit down, back supported, feet flat on the floor, arm resting on a table at heart level;
• rest for five minutes before measuring, without talking or moving during the reading;
• avoid coffee, smoking, and exercise in the half hour beforehand.

Home monitoring avoids two common pitfalls. The first is “white coat hypertension”: blood pressure rises at the doctor's office due to nervousness, while it is normal at home. The second is “masked hypertension,” the reverse situation: normal blood pressure at the doctor's office but elevated in daily life, which goes unnoticed without home measurement. On the other hand, there's no need to measure your blood pressure several times a day outside these periods: blood pressure naturally varies from moment to moment, and overly frequent measurements mostly just feed anxiety.

A condition that changes with age

The prevalence of hypertension rises markedly with age, due to the gradual, natural stiffening of the arteries over time — a phenomenon that affects nearly the entire population to varying degrees as they age. This age-related change explains why blood pressure thresholds and targets can be adjusted differently in older people, a topic beyond the scope of this article but worth discussing individually with a doctor.

The role of heredity in essential hypertension

While essential hypertension has no single identifiable cause, heredity plays a significant role: having a parent with hypertension roughly doubles the risk of developing it yourself, and that risk increases further if both parents are affected. This genetic component, however, never acts alone — it interacts with lifestyle factors (salt intake, physical activity, weight, alcohol consumption) that remain modifiable. Someone with a family history of hypertension isn't doomed to develop it, but benefits from paying particular attention to these factors, which they retain real power to act on, and from getting screened earlier and more regularly than the general population.

To take your own measurements, take the “Do I have high blood pressure?” test.