What is high blood pressure?
Blood pressure is the force of blood pushing against the walls of your arteries as your heart pumps. It is written as two numbers — the systolic pressure (when the heart beats) over the diastolic pressure (when the heart rests between beats), measured in millimetres of mercury (mmHg). High blood pressure, or hypertension, means this force is consistently too high.
A reading below 120/80 mmHg is considered normal. Readings of 130/80 mmHg or higher are generally classed as high blood pressure. Because hypertension usually causes no symptoms, many people do not know they have it — which is why it is often called the silent killer and why regular checks matter.
Symptoms and why it's dangerous
Most people with high blood pressure have no symptoms at all, even when readings are dangerously high. This is what makes it so risky — it can quietly damage your arteries, heart and other organs over years without warning. Very high blood pressure can occasionally cause headaches, shortness of breath or nosebleeds, but these are not reliable signs and usually appear only once blood pressure has reached a severe level.
Left untreated, high blood pressure significantly raises the risk of heart attack, stroke, heart failure, kidney disease, vision loss and vascular dementia. The good news is that detecting and treating it early dramatically reduces these risks.
What causes high blood pressure?
For most people, there is no single cause — this is called primary hypertension, and it develops gradually over years, influenced by a mix of factors. A smaller number of people have secondary hypertension caused by an underlying condition such as kidney disease, hormonal disorders or certain medications.
Factors that raise your risk include:
- •Older age
- •A family history of high blood pressure
- •Being overweight or obese
- •A diet high in salt and low in potassium
- •Physical inactivity
- •Drinking too much alcohol
- •Smoking
- •Long-term stress
- •Being of African or African-Caribbean descent, which carries higher risk
How it's diagnosed
High blood pressure is diagnosed by measuring your blood pressure, usually on more than one occasion, because a single high reading can be caused by stress or activity. Your doctor may ask you to monitor it at home or wear a device that takes readings over 24 hours, which gives a more accurate picture and rules out white-coat hypertension, where readings rise only in a clinical setting.
Because hypertension often accompanies other risks, your doctor may also check your cholesterol, blood sugar and kidney function, and assess your overall cardiovascular risk to guide treatment decisions.
Treatment and lifestyle changes
Treatment aims to bring your blood pressure down to a healthy target and reduce your overall risk. Lifestyle changes are the foundation and are sometimes enough on their own, especially for milder hypertension. These include reducing salt, eating more fruit and vegetables, losing excess weight, exercising regularly, limiting alcohol, stopping smoking and managing stress.
When lifestyle changes are not enough, several effective and well-tolerated medications are available, and your doctor will choose based on your individual situation. Many people need more than one. Because high blood pressure is usually lifelong, ongoing monitoring and sticking with treatment are key — even when you feel completely well.
Can it be prevented?
In many cases, yes. The same habits that treat high blood pressure also help prevent it: maintaining a healthy weight, staying physically active, eating a diet rich in fruit, vegetables and whole grains while limiting salt, drinking alcohol only in moderation, not smoking and managing stress.
Knowing your numbers is the first step. Because hypertension is symptomless, getting your blood pressure checked regularly — and acting early if it creeps up — is one of the simplest and most effective things you can do for your long-term health.
Complications of untreated high blood pressure
The reason high blood pressure is taken so seriously, despite causing few symptoms, is the damage it can do silently over years. The constant extra force on your artery walls gradually harms blood vessels throughout the body and makes the heart work harder, raising the risk of several serious conditions.
Untreated or poorly controlled high blood pressure is a leading risk factor for heart attack and stroke, two of the most common causes of death and disability worldwide. It can also lead to heart failure, where the heart struggles to pump effectively, and can damage the kidneys over time, sometimes leading to chronic kidney disease. The small blood vessels of the eyes can also be affected, and there is growing evidence linking long-term high blood pressure to vascular dementia.
This long list is not meant to alarm but to explain why treatment matters even when you feel completely well. The encouraging side is that lowering blood pressure, whether through lifestyle, medication, or both, meaningfully reduces all of these risks, and the benefits begin soon after blood pressure comes under control.
Monitoring your blood pressure at home
Because blood pressure varies through the day and can rise simply from being in a clinic (so-called white-coat hypertension), monitoring at home gives a fuller, more accurate picture. Home monitoring is increasingly recommended both for diagnosis and for keeping track once you are being treated, and affordable, reliable automatic monitors are widely available.
For accurate readings, sit quietly for five minutes first, keep your back supported and feet flat, rest your arm at heart level, and avoid caffeine, exercise and smoking beforehand. Take two readings a minute apart, ideally at the same times each day, and record them. Single high readings are less important than the overall pattern, so a log over days or weeks is far more useful than any one measurement.
Sharing your home readings with your doctor or nurse helps them tailor your treatment. If your readings are consistently high, or you ever get a very high reading with symptoms such as chest pain, severe headache or breathlessness, seek medical advice promptly.