Overview
Low blood pressure, also known as hypotension, occurs when the force of blood against artery walls is too low. It is generally defined as a reading below 90/60 mm Hg.
What is considered low for one person may be normal for another. Many people with low blood pressure have no noticeable symptoms, while others experience dizziness or fainting. In some cases, low blood pressure can be life-threatening.
Causes range from simple dehydration to serious medical conditions. Identifying the cause is important so that treatment can be provided when necessary.
Types of Low Blood Pressure
Orthostatic hypotension (postural hypotension)
A sudden drop in blood pressure when standing up from sitting or lying down. Common causes include dehydration, prolonged bed rest, pregnancy, certain medical conditions, and some medications. It is especially common in older adults.
Postprandial hypotension
A drop in blood pressure 1 to 2 hours after eating. It most often affects older adults, particularly those with high blood pressure or Parkinson’s disease and other disorders of the autonomic nervous system. Symptoms may be reduced by eating small, low-carbohydrate meals, drinking more water, and avoiding alcohol.
Neurally mediated hypotension
Blood pressure drops after standing for long periods. This type mainly affects young adults and children and may result from miscommunication between the heart and brain.
Multiple system atrophy with orthostatic hypotension
A rare disorder that affects the autonomic nervous system and is characterized by very high blood pressure when lying down. It is also known as Shy-Drager syndrome.
Symptoms of Low Blood Pressure
Common symptoms include:
- Blurred or fading vision
- Dizziness or lightheadedness
- Fainting
- Fatigue
- Trouble concentrating
- Nausea
A sudden fall in blood pressure can be dangerous. Even a drop of 20 mm Hg in systolic pressure may cause dizziness or fainting and larger drops can be life-threatening, especially with serious bleeding, infection, or severe allergic reaction.
Extreme low blood pressure can lead to shock. Symptoms of shock include:
- Confusion (especially in older adults)
- Cold, clammy skin
- Pale skin
- Rapid, shallow breathing
- Weak and rapid pulse
When to See a Doctor
Seek emergency care (call 911 or local emergency services) if you have signs of extremely low blood pressure or shock.
Blood pressure is usually considered too low only when it causes symptoms. Occasional mild dizziness or lightheadedness has many possible causes and should be evaluated by a healthcare professional.
If you frequently have low readings but feel fine, your doctor may simply monitor you during routine visits. Keeping a log of symptoms, their timing, and your activity at the time can help with diagnosis.
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