What Is Low Blood Pressure?
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Medically reviewed by Keri Peterson, MD
Low blood pressure (hypotension) is the opposite of high blood pressure (hypertension). Normal blood pressure readings are typically between 90/60 and 120/80 mm Hg (millimeters of mercury). The top and bottom numbers of a blood pressure reading represent systolic and diastolic pressure, respectively. Having a top number below 90 or a bottom number under 60 is considered low blood pressure.
This article explains why some low blood pressure (LBP) readings below 90/60 mm Hg are considered normal, what makes LBP problematic for some, how to distinguish serious symptoms from those that are not, when to seek emergency medical treatment, and more.
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Low Blood Pressure Symptoms
Symptoms associated with hypotension may include:
Light-headedness (presyncope)
Fainting (syncope)
Abnormal heart rhythm (arrhythmia)
Many people with chronic low blood pressure under 90/60 mm Hg are asymptomatic or experience mild, barely noticeable symptoms. However, if you experience any of the above symptoms associated with low blood pressure, speak to a healthcare provider promptly.
Dangerous Low Blood Pressure: What’s Considered Serious?
When determining if your low blood pressure is serious or dangerous, it's impossible to take a one-size-fits-all approach based solely on your systolic and diastolic numbers. People respond differently to LBP. According to the American Heart Association, most healthcare providers only consider chronically low blood pressure dangerous in people experiencing noticeable LBP symptoms.
Top and bottom blood pressure numbers that are considered normal and safe for one person may be abnormal and dangerous for someone else. Because there isn't a specific number that means blood pressure is dangerously low, it's important for every person who experiences hypotensive symptoms to speak with a healthcare provider. LBP should be assessed on a case-by-case basis.
For example, in some people, having chronically low blood pressure slightly under 90/60 mm Hg doesn't trigger any negative symptoms and is consistent for them. Conversely, someone else with the exact same top and bottom numbers could experience potentially dangerous LBP symptoms like dizziness, blurry vision, or fainting when their blood pressure falls below 90/60 mm Hg.
Sudden blood pressure drops caused by blood loss (hemorrhaging) or severe infection should always be treated as emergencies. When abnormally low blood pressure triggers acute circulatory failure, it causes shock, a serious life-threatening condition that requires immediate medical attention. Septic shock caused by an infection is also marked by dangerously low blood pressure.
The greatest danger associated with severely low blood pressure is inadequate tissue perfusion. This means that vital organs don't get enough blood flow and oxygen, called hypoperfusion. It can be deadly if LBP causes insufficient blood flow and subsequent hypoperfusion. Although extremely low blood pressure can be dangerous, hypotension doesn't always lead to organ hypoperfusion.
Symptoms associated with different types of shock include:
Inadequately low blood pressure
Blue, gray, or purple skin (cyanosis)
Clammy skin
Cold sweats (diaphoresis)
Cool extremities
Rapid, shallow breathing (tachypnea)
Slow heart rate (bradycardia)
Weak pulse
Altered mental states
Abnormally low urine output (oliguria)
When low blood pressure causes any symptoms of shock, it should be treated as an emergency. If someone experiences a dangerous drop in blood pressure and goes into shock, call 911 right away.
What Causes Blood Pressure to Drop?
Changes in body position, such as standing up quickly, commonly cause blood pressure to drop. This type of low blood pressure is called postural (orthostatic) hypotension. Orthostatic hypotension is the most common form of LBP.
Other factors that may cause low blood pressure include:
Lying in bed for long periods (bed rest)
Eating a big meal (postprandial hypotension)
Problems with the autonomic nervous system (regulates involuntary processes such as breathing rate)
Parkinson's disease (a neurodegenerative movement disorder)
Abnormal heart rhythm (cardiac arrhythmias)
Blood loss from an injury (hemorrhage)
Testing to Diagnose Low Blood Pressure
Routine blood pressure tests can diagnose low blood pressure, which is considered a BP reading below 90/60 mm Hg. Blood tests, urine samples, and imaging are also used to diagnose LBP. If you have low blood pressure and faint often, you may undergo a tilt table test to aid in diagnosis.
In medical emergencies, healthcare providers often use something called mean arterial pressure (MAP) to monitor and diagnose low blood pressure in critically ill patients.
MAP readings above 65 are a target that usually means blood pressure isn't dangerously low. Notably, prolonged MAP readings below 65 for more than two hours can be dangerous and are associated with higher mortality (death) rates.
Some studies have found a correlation between low blood pressure and increased risk of ischemic stroke (a condition in which blood flow to the brain is interrupted or reduced) and higher mortality in people with LBP after a stroke.
Low Blood Pressure Treatment
People who have low blood pressure based on a systolic reading below 90 or a a diastolic reading below 60 but are asymptomatic (with no or very mild symptoms) typically don't require treatment.
The following measures may help if you have low blood pressure with notable symptoms:
Getting up more slowly
Increasing salt intake
Drinking more water
Wearing compression stockings
Not standing for long periods
Always talk to a healthcare provider before trying any of these treatments. In cases of severe low blood pressure, medications or other treatments may be prescribed.
How to Check Low Blood Pressure at Home
Home blood pressure monitoring is a readily accessible and affordable way to check low blood pressure on your own. There are lots of easy-to-use monitoring products available for home use.
If you have severe low blood pressure symptoms, a healthcare provider may recommend an ambulatory blood pressure monitoring device that records your blood pressure constantly over 24 hours. Unlike inaccurate "whitecoat" readings that often occur during stressful medical visits, ambulatory monitoring provides highly accurate blood pressure readings at home and as you go about daily life.
What to Do During a Sudden Drop in Blood Pressure
The best thing to do during a sudden drop in blood pressure is to sit down. Sudden blood pressure drops can lead to fainting and falls; sitting helps avoid this. You can also try lying down and elevating your legs above the heart, which increases cardiac output and boosts blood pressure.
If a sudden drop in blood pressure causes someone to lose consciousness or go into shock, call 911 immediately.
Outlook
In general, the outlook for low blood pressure is good. Many people go about their daily lives with chronically low blood pressure without experiencing any symptoms. Whereas high blood pressure is associated with poor outcomes, having LBP isn't necessarily a bad thing.
However, if low blood pressure does cause symptoms, it's important to speak with a healthcare provider right away and to seek medical attention immediately if a sudden drop in blood pressure triggers shock.
Summary
Low blood pressure is considered a reading of below 90/60 mm Hg. Although having a top number below 90 or a bottom number below 60 is technically considered LBP, many people have chronically low blood pressure without experiencing negative symptoms. If low blood pressure doesn't cause symptoms, it usually doesn't require treatment.
However, if LBP does cause symptoms or results in episodes of postural hypotension, making you dizzy or light-headed when becoming upright too quickly, it can result in fainting or dangerous falls. Very sudden drops in blood pressure caused by accidents or severe infection can cause shock or sepsis and should always be treated as medical emergencies.
