Patient information from BMJ

High blood pressure: what is it?

Last published:May 01, 2025

High blood pressure is very common. You may not realise you have high blood pressure until a doctor or nurse tells you, because there are usually no symptoms. But having high blood pressure increases your chance of serious health problems, including heart attacks and strokes.

There are treatments available. Your doctor will also recommend things you can do yourself to try and reduce your blood pressure and help you stay healthy.

What is high blood pressure?

Your blood pressure rises and falls slightly throughout the day and night. But when it stays above a certain level, it's called high blood pressure. High blood pressure is also called hypertension.

Your blood needs to be under some pressure to keep it moving around your body. But if the pressure is too high, over time it can damage your blood vessels and cause problems.

You are more likely to have high blood pressure if you:

• are over 60 years old

• have a close relative with high blood pressure

• have certain medical conditions (such as diabetes, kidney disease, or sleep apnoea)

• are black

• are overweight

• drink moderate to high amounts of alcohol, or

• don’t exercise, or have a low level of fitness.

What are the symptoms?

Most people with high blood pressure don't get any symptoms. You can't feel when your blood pressure goes up. Although occasionally people with very high blood pressure have bad headaches or changes to their eyesight. Most people only find out they have high blood pressure after having it checked.

How will my blood pressure be checked?

Your doctor will measure your blood pressure using an inflatable cuff that goes around your upper arm. You’ll need to have your blood pressure measured on two or more occasions to make sure it’s not just a one-off high reading. You should also have it measured in both arms.

Doctors measure blood pressure with two numbers:

• The first number is called the systolic pressure. It measures the highest level of pressure in your blood. This is when your heart beats to pumps blood out around your body.

• The second number is called the diastolic pressure. This is the lowest pressure in your blood vessels. It is measured when your heart relaxes between beats and fills up with blood.

Your doctor will probably describe your blood pressure using these two numbers: for example, '140 over 90'.

Usually, doctors will say you have high blood pressure if either your first number is higher than 140 or your second number is higher than 90.

If your reading is high, your doctor may recommend that you measure your own blood pressure at home.

Another option is to wear a device that measures your blood pressure several times over the course of one day. This is called ambulatory blood pressure monitoring.

Blood pressure goes up and down during the day, so home and ambulatory monitoring can help confirm whether your blood pressure is high all the time.

Also, some people feel nervous when having their blood pressure taken by a doctor or nurse, and this can lead to their blood pressure being unusually high.

This is often called 'white coat hypertension'. It's named after the white coats that healthcare professionals sometimes wear. Measuring your blood pressure yourself at home can help confirm your blood pressure when you are relaxed.

What will happens next?

If you have high blood pressure, your doctor will probably want to do some blood tests to check for other medical conditions. This will include checking your kidneys and heart, and whether you have diabetes.

If your blood pressure stays too high, it damages your blood vessels. And it puts strain on other parts of your body, such as your heart, brain and kidneys. This can increase your risk of very serious problems such as heart attacks, strokes, heart failure, eye problems, and kidney failure.

But not everybody with high blood pressure will get these problems. It depends on several things, including: 

• how high your blood pressure is

• how long you've had high blood pressure

• whether you have other health problems (such as high cholesterol or diabetes)

• whether you manage to successfully control your blood pressure by taking your medicines and making changes to your lifestyle. This may include exercising regularly and avoiding drinking too much alcohol.

The good news is that the harmful effects of high blood pressure don't happen suddenly. They usually take many years to develop. And if you control your high blood pressure you can reduce the chance that they will ever happen.

Where to get more help

There are groups that provide advice and support for people with high blood pressure. Your doctor or nurse may be able to help you find support in your area, or you can search online.

There is more information on ways to control your blood pressure in our patient information: High blood pressure: what are the treatment options?