Primary, or essential, hypertension is the most common form of high blood pressure, occurring in about 90 to 95 percent of cases. There is no known specific cause. However, there are several factors that – alone or in combination – can increase the risk of developing primary hypertension. These include:

Evidence also continues to build linking sodium intake with high blood pressure. Salt affects blood pressure because it causes the body to retain more water.

Normally, the kidneys flush this excess salt and water from the body. However, kidneys that are not functioning properly are unable to expel it sufficiently from the body, which will lead to fluid retention. Because the function of the kidneys is so closely tied with the body’s circulatory system, changes in blood pressure will prompt the kidneys to make an adjustment. If the kidneys malfunction and there is excess fluid in the system, hypertension can result.

Conversely, if high blood pressure exists, the kidneys may slow, and excess salt and fluid will collect in the body, adding further to the hypertension problem.

Underlying heart damage or dysfunction, including atherosclerosis, or a buildup of plaque within the artery walls, may add to the increased blood force against the artery walls. The pressure of the blood through these restricted passageways rises because of a lack of space. Higher blood pressure can also result if there is more blood relative to the size of the blood vessel.

White coat hypertension refers to mild hypertension that occurs in a physician's office, but does not occur at home. Generally, this is thought to be related to stress associated with the test itself. Previously, many experts considered white coat hypertension to be harmless. However, newer research is showing that white coat hypertension shares some similarities with essential hypertension and may slightly increase the risk of future heart problems.