Blood pressure is considered low when it drops below 90/60 mmHg. For some people, this is completely normal and causes no problems. For others, it signals that something in the body isn’t maintaining the delicate balance of blood flow, heart rate, and blood vessel tension that keeps pressure steady. The reasons range from everyday triggers like dehydration to serious medical conditions that need prompt attention.
How Your Body Maintains Blood Pressure
Understanding why blood pressure drops starts with understanding how your body keeps it stable. Your cardiovascular system constantly adjusts three things: how hard your heart pumps, how much blood is circulating, and how tight or relaxed your blood vessels are. Sensors called baroreceptors, located in your arteries, monitor pressure in real time and send signals to your brain, which then fine-tunes your heart rate and blood vessel tension to compensate for changes.
When any part of this system fails or gets overwhelmed, blood pressure falls. That could mean your heart isn’t pumping forcefully enough, you don’t have enough fluid in your bloodstream, your blood vessels are too relaxed, or the signaling between your brain and cardiovascular system misfires. Most causes of low blood pressure fit into one of these categories.
Dehydration and Low Blood Volume
The most common everyday cause of low blood pressure is simply not having enough fluid in your system. When you’re dehydrated from illness, heat, exercise, or not drinking enough water, your total blood volume drops. With less blood circulating, your heart can’t generate the same pressure with each beat. Vomiting, diarrhea, heavy sweating, and excessive urination all pull fluid out of your bloodstream and can cause a noticeable pressure drop.
Significant blood loss from an injury, surgery, or internal bleeding creates the same problem on a larger scale. The heart literally doesn’t have enough blood to pump effectively, and pressure falls rapidly. This is called hypovolemia, and in severe cases it prevents the heart from delivering blood to organs throughout the body.
Medications That Lower Pressure Too Much
Drugs designed to treat high blood pressure sometimes overshoot the mark. Blood pressure medications, water pills (diuretics), and heart medications can all push your numbers lower than intended, especially when you first start them or when doses change. This is one of the most frequent causes of low blood pressure in older adults.
Other medications cause low blood pressure as an unintended side effect. Certain antidepressants, drugs for Parkinson’s disease, and erectile dysfunction medications can all relax blood vessels or affect heart rate enough to lower pressure. If your blood pressure dropped around the same time you started or adjusted a medication, that connection is worth exploring with your prescriber.
Standing Up Too Fast
If your blood pressure drops mainly when you go from sitting or lying down to standing, that’s called orthostatic hypotension. It’s diagnosed when standing causes a drop of 20 mmHg or more in the top number, or 10 mmHg or more in the bottom number, within about three minutes.
Here’s what happens: when you stand, gravity pulls roughly 500 to 800 mL of blood down into the veins of your legs. Normally, your baroreceptors detect this shift instantly, and your nervous system responds by tightening blood vessels and speeding up your heart rate to compensate. When that reflex is too slow or too weak, pressure drops and you feel lightheaded or dizzy. Dehydration, prolonged bed rest, aging, diabetes, and certain neurological conditions can all blunt this reflex. Medications for high blood pressure are another frequent culprit.
Blood Pressure Drops After Eating
Some people experience a noticeable pressure drop within one to two hours after a meal. This is called postprandial hypotension, and it’s surprisingly common in older adults. Research reviews estimate that about 40% of people between ages 65 and 86 experience it.
After you eat, your body redirects blood flow to your digestive system to help break down food. Normally, your heart rate increases and blood vessels elsewhere in your body tighten to keep overall pressure stable. When those compensating mechanisms don’t kick in strongly enough, pressure falls. Large, carbohydrate-heavy meals tend to trigger bigger drops. Eating smaller, more frequent meals and avoiding alcohol with food can reduce the effect.
Heart Conditions
Your heart is the pump driving the whole system, so problems with the heart itself directly affect blood pressure. An unusually slow heart rate means less blood gets pushed out per minute. Heart valve problems can reduce the efficiency of each pump cycle. Heart failure, where the heart muscle is weakened, means each contraction pushes out less blood than it should. A heart attack can suddenly impair pumping ability.
These cardiac causes tend to produce low blood pressure alongside other symptoms like fatigue, shortness of breath, chest discomfort, or swelling in the legs. Persistently low blood pressure with these kinds of symptoms points toward the heart as the source.
Hormonal and Endocrine Problems
Several glands in your body produce hormones that directly regulate blood pressure, and when they malfunction, pressure can drop. The adrenal glands, which sit on top of your kidneys, produce a hormone called aldosterone that controls how much sodium and potassium your body retains. This balance directly affects blood volume and vessel tension.
In Addison’s disease, the adrenal glands don’t produce enough of these hormones. Low blood pressure, particularly when standing up, is one of the early symptoms. People with Addison’s disease often experience dizziness, fatigue, and fainting along with the pressure drop. Thyroid disorders, particularly an underactive thyroid, and low blood sugar can also contribute to lower-than-normal blood pressure.
Nervous System Misfires
Sometimes the signaling system that controls blood pressure simply gets it wrong. In a condition called neurally mediated hypotension, standing for long periods triggers a paradoxical response. Your brain detects that less blood is returning to the heart and, instead of correctly compensating, sends a signal that actually drops your heart rate and relaxes your blood vessels. The result is a sudden pressure drop that can cause lightheadedness or fainting.
This type of fainting episode is especially common in younger, otherwise healthy people. It can be triggered by standing in one place for a long time, being in a hot environment, or experiencing strong emotional stress. The underlying mechanism involves your heart contracting vigorously on a relatively empty chamber, which sends confusing signals back to the brain and triggers an inappropriate relaxation response.
Serious and Emergency Causes
Some causes of low blood pressure are medical emergencies. In sepsis, a severe infection triggers widespread inflammation that causes blood vessels throughout the body to dilate all at once. Blood also leaks out of capillaries into surrounding tissue. The combined effect is a dramatic pressure drop that can starve organs of oxygen.
Severe allergic reactions (anaphylaxis) produce a similar rapid blood vessel relaxation, along with swelling that can obstruct breathing. Both conditions cause blood pressure to plummet within minutes and require immediate emergency treatment. Signs that low blood pressure is an emergency include confusion, cold or clammy skin, rapid shallow breathing, a weak and fast pulse, and losing consciousness.
When Low Blood Pressure Is Just Normal
Not every reading below 90/60 is a problem. Some people, particularly those who are young, physically fit, or have a naturally smaller build, run low blood pressures their entire lives without any symptoms. Athletes in particular often have lower resting blood pressure because their hearts pump more efficiently.
The key distinction is whether low blood pressure causes symptoms. If you feel fine, a reading on the lower side is generally not a concern. But if you’re regularly experiencing dizziness, blurred vision, nausea, fatigue, or difficulty concentrating alongside low readings, something is likely interfering with your body’s ability to maintain adequate blood flow, and it’s worth identifying the cause.