Low blood pressure, or hypotension, occurs when a person's blood pressure measures below 90 for systolic and 60 for diastolic, according to WebMD. Having just one number below these given figures is enough for a person to have hypotension.
In healthy people who have no symptoms, hypotension is usually not threatening and requires no treatment, notes WebMD. However, the risks for developing complications due to hypotension increase as a person ages, in part because of the normal plaque buildup in blood vessels. Hypotension may be a sign of an underlying condition, especially in the elderly, where it can prevent blood from reaching major organs such as the lungs or brain.