Blood pressure typically increases throughout life, from infancy to older adulthood. Because most babies and children aren't at risk for blood pressure problems, doctors are unlikely to measure children's blood pressure routinely. For all adults, though, regardless of age, a normal blood pressure is considered to be less than 120/80.
Normal Blood Pressure in Babies and Children
A "normal" blood pressure changes throughout childhood -- it's lowest in infants and gradually increases throughout childhood. Unless your child is at risk for a blood pressure problem, however -- for example, from kidney disease or diabetes -- her doctor is unlikely to take blood pressure readings at all. Determining normal blood pressure in children is a bit complicated, and it depends on the child's size and age. One rule of thumb doctors use, though, is this: a child is considered to have "prehypertension" if she has a blood pressure greater than 90 percent of children of similar age and size, and to have "hypertension" if she has a blood pressure greater than 95 percent.
Normal Blood Pressure in Adolescents, Adults and Older Adults
It may seem surprising, given that blood pressure naturally increases with age, but a normal blood pressure is considered the same for all adolescents, adults and older adults: below 120/80. The first of those two numbers, the systolic blood pressure, reflects the pressure in the blood vessels when the heart is contracting and exerting maximum pressure. The second number, the diastolic blood pressure, reflects the pressure in the blood vessels when the heart is at rest, between contractions. If either one of those two numbers is too high, the blood pressure is not considered normal.
Higher Than Normal: Prehypertension and Hypertension
Adults are considered to have prehypertension if their systolic blood pressure reading is consistently above 120 but below 140, or if their diastolic blood pressure is above 80 or below 90. People with prehypertension are likely to progress to having hypertension unless they take some measures to lower their blood pressure. If you have a blood pressure greater than 140/90, you are considered to have hypertension. Your doctor might recommend certain lifestyle habits that can help lower your blood pressure, such as maintaining a healthy weight, exercising regularly, quitting smoking, and limiting your intake of alcohol and salt. Depending on how high your blood pressure is and what other health problems you have, your doctor might also recommend blood pressure medication.
Low Blood Pressure
Although it's a less common problem than high blood pressure, your blood pressure might become lower than normal at any age. Some people have naturally low blood pressure without experiencing any symptoms, but for others, a low systolic blood pressure -- typically lower than 90 -- can result in symptoms such as dizziness, lightheadedness or fainting. Low blood pressure is typically caused by another problem, such as dehydration, a sudden blood loss, or a side effect of drugs, and your doctor will recommend treatment depending on the cause.
What Can Make a Normal Blood Pressure Abnormal?
At any age, certain factors can lead to a deceptively high blood pressure reading, even in people with a normally healthy blood pressure. For example, caffeine and tobacco can lead to higher readings; so can being woken up suddenly before a reading, or exercising right before a reading. Stress can also elevate a normal reading. Some people experience stress whenever they're in a doctor's office, leading to higher-than-normal readings -- so-called white-coat hypertension. These people often find it helpful to monitor their blood pressure at home for more accurate results.