A blood pressure reading is generally considered low when the top number is below 90 or the bottom number is below 60 mm Hg. However, a low number alone does not always mean something is wrong: some people naturally have low readings and feel well. Low blood pressure needs attention when it causes symptoms such as dizziness or fainting; a sudden drop with signs of shock is an emergency.
What Blood Pressure Reading Is Considered Too Low?
In adults, low blood pressure, medically called hypotension, is generally defined as a reading below 90/60 mm Hg. The measurement contains two numbers: systolic pressure, which is the top number recorded when the heart beats, and diastolic pressure, which is the bottom number recorded between heartbeats.
A reading below 90 for the systolic pressure or below 60 for the diastolic pressure may be considered low. Both numbers do not need to fall below these values for a reading to be considered low. According to Mayo Clinic, however, what counts as too low for one person may be acceptable for another, depending on their usual blood pressure and whether they experience symptoms.
For example, someone who regularly records a reading around 88/58 mm Hg and feels well may not need treatment. In contrast, a person whose blood pressure suddenly falls from their usual level and who becomes dizzy or faint may need medical assessment, even if the new reading is not extremely low.
When Does Low Blood Pressure Become Dangerous?
The main concern is whether blood pressure is low enough to interfere with the delivery of blood to the brain and other organs. A reading that remains below 90/60 mm Hg may be harmless for some people, but a sudden fall or a low reading accompanied by concerning symptoms deserves greater attention.
Symptoms that can occur with low blood pressure include:
- Dizziness or lightheadedness, especially when standing up.
- Blurred or fading vision.
- Unusual weakness or fatigue.
- Nausea.
- Difficulty concentrating or confusion.
- Fainting or feeling as though you might pass out.
According to MedlinePlus, these symptoms can occur with low blood pressure, although they may also have other causes. Persistent dizziness, repeated fainting, or symptoms that interfere with everyday activities should be assessed by a healthcare professional.
Which Low Blood Pressure Symptoms Require Emergency Care?
A sudden, severe drop in blood pressure can lead to shock, a life-threatening condition in which the body's organs do not receive enough blood and oxygen. Warning signs may include:
- Confusion or a marked change in alertness.
- Cold, pale, or clammy skin.
- Rapid, shallow breathing.
- A weak, rapid pulse.
- Fainting or collapse, particularly with other warning signs.
The Merck Manual identifies shock as a medical emergency. If someone has signs of shock, call your local emergency number immediately rather than waiting to see whether their blood pressure improves. Do not delay emergency care to repeat a measurement.
Why Might Your Blood Pressure Reading Be Low?
Several factors can cause low blood pressure, and the reason matters when deciding whether treatment is needed. A low reading may be temporary, related to a person's usual blood pressure, associated with medication, or linked to an underlying health problem.
- Dehydration: Not drinking enough fluid, vomiting, diarrhea, or heavy sweating can reduce the amount of fluid circulating in the body.
- Blood loss: Significant bleeding can cause blood pressure to fall, sometimes rapidly.
- Medicines: Blood pressure medicines, diuretics, and certain other prescription medicines may lower blood pressure.
- Heart conditions: Some heart rhythm problems, heart valve disorders, and heart failure can contribute to low readings.
- Hormonal or other medical conditions: Certain endocrine disorders, diabetes-related problems, and severe infections may affect blood pressure.
- Pregnancy: Changes in blood vessels during pregnancy can lower blood pressure, particularly earlier in pregnancy.
- Changes in position or after meals: Blood pressure may fall when a person stands up or, in some people, after eating.
These are possible explanations rather than a way to identify the cause from a blood pressure number alone. A healthcare professional may review your medical history, medicines, symptoms, and recent illnesses to determine whether further assessment is needed.
Why Does Blood Pressure Drop When You Stand Up?
Blood pressure can fall briefly when you move from lying down or sitting to standing. When this drop persists, it may be associated with a condition called orthostatic hypotension, also known as postural hypotension.
Symptoms can include lightheadedness, dizziness, blurred vision, or fainting after standing. Dehydration, prolonged bed rest, certain medicines, and some medical conditions may contribute to this problem. According to Mayo Clinic's guidance on orthostatic hypotension, frequent symptoms on standing warrant medical evaluation.
This pattern is more common in older adults. Some people also experience a blood pressure drop after eating, particularly older adults and those with certain underlying conditions. If dizziness occurs repeatedly after standing or meals, note when it happens and discuss the pattern with your healthcare professional.
How Should You Recheck a Low Blood Pressure Reading?
If you obtain an unexpectedly low reading but feel well, repeat the measurement correctly before drawing conclusions from a single result. Temporary changes, body position, and measurement technique can affect the number.
- Sit quietly for at least five minutes before measuring.
- Keep your back supported, feet flat on the floor, and legs uncrossed.
- Place the cuff on your bare upper arm, using the correct cuff size.
- Support your arm on a flat surface at heart level.
- Stay still and avoid talking while the device measures your blood pressure.
- Take two readings about one minute apart and record both results.
The American Heart Association recommends proper positioning, an appropriately sized cuff, and repeated measurements to help obtain reliable home readings. Record the date, time, symptoms, and any relevant activity so a healthcare professional can review the pattern.
If you feel dizzy or faint, sit or lie down immediately to reduce the risk of falling. Raising your feet may help if it is comfortable and safe to do so. If symptoms persist, recur, or accompany a repeatedly low reading, seek medical advice. Do not postpone urgent assessment when serious symptoms are present.
When Should You Contact a Healthcare Professional?
Arrange a medical assessment if your readings are repeatedly low and you experience dizziness, weakness, blurred vision, or fainting. It is also important to seek advice if your blood pressure has dropped noticeably from its usual level, symptoms are becoming more frequent, or the readings began after starting or changing a medicine.
During the assessment, a healthcare professional may check your blood pressure more than once, including in different positions when appropriate. They may also review your medicines, examine you, and consider tests based on your symptoms and medical history. Treatment depends on the cause; some people require no treatment, while others may need a change in medication or care for an underlying condition.
Do not stop or change prescribed medicines on your own, even if you suspect they are lowering your blood pressure. Discuss the readings with the prescribing clinician, who can decide whether an adjustment is appropriate.
Does the 90/60 mm Hg Threshold Apply to Children?
The commonly used threshold of below 90/60 mm Hg is a general guide for adults, not a universal cutoff for every age group. In babies and children, what counts as low blood pressure depends on age and other clinical factors. A reading should therefore be interpreted using appropriate pediatric ranges rather than adult thresholds alone.
Children's Health explains that low blood pressure in children is assessed against age-specific expectations. If a child has a low reading accompanied by fainting, unusual weakness, confusion, signs of dehydration, or other concerning symptoms, seek prompt medical assessment. Severe symptoms such as cold, clammy skin or rapid, shallow breathing require emergency care.
The Bottom Line on Low Blood Pressure Readings
For adults, blood pressure below 90/60 mm Hg is generally considered low, but the number does not tell the whole story. A naturally low reading without symptoms may be normal for that person. A sudden drop, repeated symptoms, or signs of poor circulation need closer attention. Recheck unexpected readings using proper technique, keep a record of recurring symptoms, and seek emergency care if signs of shock develop.