Essential hypertension (high blood pressure not as a result from another medical condition) is due to decreased compliance/elasticity of the walls of your blood vessels. Think of a balloon: if you blow air into the balloon it expands nicely. If you paint the balloon so that it can't expand and fill it with the same amount of air, the pressure in the balloon will be much higher. These changes happen naturally as we age and are exacerbated by numerous factors, particularly smoking and atherosclerosis. This is far and away the most common type of hypertension.
Similarly, an increase in effective circulating volume will also lead to high blood pressure (adding more and more air into the balloon). Eating a lot of salt increases the osmotic pressure in your blood vessels, drawing in excess fluid, leading to high blood pressure. That's why limiting salt intake is as important, if not more important, than taking medications to treat high blood pressure.
Secondary hypertension is elevated blood pressure as a result of another medical problem. This is much more rare. Possible causes of secondary hypertension include renal artery stenosis (narrowing of the arteries that deliver blood to the kidneys), pheochromocytoma (a tumor of the adrenal gland), and a dozen other things. Your doctor would suspect this if your blood pressure is not responding to the usual therapy.
High blood pressure runs in some families.
Unhealthy eating habits, plus lack of exercise.
The exact causes of high blood pressure?are not known. Several factors and conditions may play a role in its development, including:
Being overweight or obese
Lack of physical activity
Too much salt in the diet
Too much alcohol consumption (more than 1 to 2 drinks per day)
Family history of high blood pressure
Chronic kidney disease
Adrenal and thyroid disorders