What is high blood pressure?

In many people with high blood pressure, a single specific cause is not known. This is called essential or primary high blood pressure. Research is continuing to find causes. In some people, high blood pressure is the result of another medical problem or medication. When the cause is known, this is called secondary high blood pressure.
This section ? National Heart, Lung, and Blood Institute
What is high blood pressure? A blood pressure of 140/90 or higher is considered high blood pressure. Both numbers are important. If one or both numbers are usually high, you have high blood pressure. If you are being treated for high blood pressure, you still have high blood pressure even if you have repeated readings in the normal range. There are two levels of high blood pressure: Stage 1 and Stage 2 (see the chart below). Categories for Blood Pressure Levels in Adults* (In mmHg, millimeters of mercury)
Category
Systolic(Top number)
Diastolic(Bottom number)
Normal
Less than 120
Less than 80
Prehypertension
120-139
80-89
High Blood Pressure
Systolic
Diastolic
Stage 1
140-159
90-99
Stage 2
160 or higher
100 or higher* For adults 18 and older who:
Are not on medicine for high blood pressure
Are not having a short-term serious illness
Do not have other conditions such as diabetes and kidney disease Note: When systolic and diastolic blood pressures fall into different categories, the higher category should be used to classify blood pressure level. For example, 160/80 would be stage 2 high blood pressure. There is an exception to the above definition of high blood pressure. A blood pressure of 130/80 or higher is considered high blood pressure in persons with diabetes and chronic kidney disease.