Low blood pressure (hypotension)Low to low blood pressure pressure might seem desirable, and for some people, it to low blood pressure no problems. Blold, for many people, abnormally low blood pressure hypotension can cause dizziness and fainting. In severe cases, low blood pressure can be life-threatening. A blood pressure reading lower than 90 millimeters of mercury mm Hg for the top number systolic or 60 mm Hg for the bottom number diastolic is generally considered low blood pressure. The causes of predsure blood pressure can range from dehydration to serious medical or surgical disorders.
Low Blood Pressure Causes, Symptoms, Normal Ranges, & More
Low blood pressure might seem desirable, and for some people, it causes no problems. However, for many people, abnormally low blood pressure hypotension can cause dizziness and fainting. In severe cases, low blood pressure can be life-threatening. A blood pressure reading lower than 90 millimeters of mercury mm Hg for the top number systolic or 60 mm Hg for the bottom number diastolic is generally considered low blood pressure.
The causes of low blood pressure can range from dehydration to serious medical or surgical disorders. It's important to find out what's causing your low blood pressure so that it can be treated. For some people, low blood pressure signals an underlying problem, especially when it drops suddenly or is accompanied by signs and symptoms such as:. If you have consistently low blood pressure readings but feel fine, your doctor is likely just to monitor you during routine exams.
Even occasional dizziness or lightheadedness may be a relatively minor problem — the result of mild dehydration from too much time in the sun or a hot tub, for example.
Still, it's important to see your doctor if you have signs or symptoms of hypotension because they can point to more-serious problems. It can be helpful to keep a record of your symptoms, when they occur and what you're doing at the time. Blood pressure is a measurement of the pressure in your arteries during the active and resting phases of each heartbeat.
Throughout the day, blood pressure varies, depending on body position, breathing rhythm, stress level, physical condition, medications you take, what you eat and drink, and time of day. Blood pressure is usually lowest at night and rises sharply on waking.
What's considered low blood pressure for you may be normal for someone else. Most doctors consider blood pressure too low only if it causes symptoms. Some experts define low blood pressure as readings lower than 90 mm Hg systolic or 60 mm Hg diastolic. If either number is below that, your pressure is lower than normal. A sudden fall in blood pressure can be dangerous. A change of just 20 mm Hg — a drop from systolic to 90 mm Hg systolic, for example — can cause dizziness and fainting when the brain fails to receive an adequate supply of blood.
And big plunges, such as those caused by uncontrolled bleeding, severe infections or allergic reactions, can be life-threatening. Doctors often break down low blood pressure hypotension into categories, depending on the causes and other factors.
Some types of low blood pressure include:. Low blood pressure on standing up orthostatic, or postural, hypotension. This is a sudden drop in blood pressure when you stand up from a sitting position or after lying down. Gravity causes blood to pool in your legs when you stand. Ordinarily, your body compensates by increasing your heart rate and constricting blood vessels, thereby ensuring that enough blood returns to your brain.
But in people with orthostatic hypotension, this compensating mechanism fails and blood pressure falls, leading to dizziness, lightheadedness, blurred vision and even fainting. Orthostatic hypotension can occur for various reasons, including dehydration, prolonged bed rest, pregnancy, diabetes, heart problems, burns, excessive heat, large varicose veins and certain neurological disorders. A number of medications also can cause orthostatic hypotension, particularly drugs used to treat high blood pressure — diuretics, beta blockers, calcium channel blockers and angiotensin-converting enzyme ACE inhibitors — as well as antidepressants and drugs used to treat Parkinson's disease and erectile dysfunction.
Orthostatic hypotension is especially common in older adults, but it also affects young, otherwise healthy people who stand up suddenly after sitting with their legs crossed for long periods or after squatting for a time. It's also possible to have delayed orthostatic hypotension, with signs and symptoms developing 5 to 10 minutes after a change in posture. This might be a milder form of the condition, or it could be an early stage of it.
Low blood pressure after eating postprandial hypotension. This sudden drop in blood pressure after eating affects mostly older adults. Blood flows to your digestive tract after you eat. Ordinarily, your body increases your heart rate and constricts certain blood vessels to help maintain normal blood pressure. But in some people these mechanisms fail, leading to dizziness, faintness and falls. Postprandial hypotension is more likely to affect people with high blood pressure or autonomic nervous system disorders such as Parkinson's disease.
Lowering the dose of blood pressure drugs and eating small, low-carbohydrate meals might help reduce symptoms. Low blood pressure hypotension can occur in anyone, though certain types of low blood pressure are more common depending on your age or other factors:. Even moderate forms of low blood pressure can cause dizziness, weakness, fainting and a risk of injury from falls.
And severely low blood pressure can deprive your body of enough oxygen to carry out its normal functions, leading to damage to your heart and brain. Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. This content does not have an English version. This content does not have an Arabic version. Overview Low blood pressure might seem desirable, and for some people, it causes no problems.
Request an Appointment at Mayo Clinic. National Heart, Lung, and Blood Institute. Kaufman H, et al. Mechanisms, causes and evaluation of orthostatic hypotension. Understanding blood pressure readings. Kaplan NM, et al. Ambulatory and home blood pressure monitoring and white coat hypertension. Treatment of orthostatic and postprandial hypotension. Related Daily water requirement Symptom Checker What is blood pressure? Mayo Clinic Marketplace Check out these best-sellers and special offers on books and newsletters from Mayo Clinic.