Postural Orthostatic Tachycardia Syndrome (POTS) doesn’t always look like much from the outside, which is part of what makes it so frustrating for the people who have it. But there are real, visible signs if you know where to look. The most recognizable is a dramatic color change in the feet and lower legs upon standing, often accompanied by visible swelling, facial flushing, and a person who looks perfectly fine while sitting but becomes pale, shaky, or unsteady the moment they stand up.
The Color Change in Your Legs
The most visually striking sign of POTS is what happens to the lower legs and feet when a person stands. Within minutes, the feet and ankles can turn a deep red, purple, or bluish color. This is called acrocyanosis, and it happens because blood pools in the lower extremities instead of circulating efficiently back up to the heart and brain. Research published in The Journal of Pediatrics found that calf volume in POTS patients increased twice as much as in healthy controls during upright posture, and it happened faster (within about 13 minutes compared to 30 minutes in controls). The correlation between increased blood flow to the legs and visible swelling was strong.
This pooling isn’t subtle. Some people describe looking down and seeing a sharp line where their skin changes from normal color above the knee to a mottled purple below it. The discoloration typically fades once the person sits or lies back down. People with POTS also tend to develop visible edema, or puffiness, in the feet and ankles. Research on vascular function in POTS has shown that resting venous pressure is higher and the threshold for edema is lower in these patients, making them especially prone to fluid collecting in the lower legs.
What a POTS Episode Looks Like
To an observer, a POTS episode often looks like someone suddenly becoming unwell after standing. The person may go pale, start sweating, grip a counter or wall for support, or need to sit or lie down urgently. Their heart may be visibly pounding in their chest or neck. They might sway, seem confused, or appear like they’re about to faint. Some people do faint, though many with POTS hover in that “pre-faint” zone without fully losing consciousness.
The defining feature is a heart rate that spikes dramatically upon standing. For a formal diagnosis, heart rate must increase by at least 30 beats per minute in adults (or 40 bpm in adolescents) within the first 10 minutes of standing, without a significant drop in blood pressure. That second part is important: unlike conditions where blood pressure crashes, POTS keeps blood pressure relatively stable while the heart races to compensate. A heart rate that jumps from 70 lying down to 110 or higher while standing, with the person looking progressively worse the longer they stay upright, is a classic picture of POTS.
Symptoms You Can’t See
Much of POTS is invisible. The racing heart, dizziness, and crushing fatigue aren’t obvious to someone watching. One of the most common complaints is “brain fog,” a term patients use to describe cognitive symptoms that go well beyond feeling a little tired. In a study evaluating brain fog in adolescents with POTS, 91% described feeling forgetful, 89% reported difficulty thinking, 88% had trouble focusing, and 88% struggled to find the right words or communicate clearly. These cognitive symptoms can look from the outside like someone is distracted or not paying attention, when in reality their brain isn’t getting adequate blood flow.
That’s the core problem in POTS. When you stand, your body compensates by increasing heart rate to push blood upward against gravity. In POTS, the autonomic nervous system overactivates, driving heart rate much higher than normal, but the compensation still falls short. The heart beats faster, yet blood flow to the brain remains inadequate. The result is a mismatch: the heart is working overtime, but the person still feels dizzy, foggy, and exhausted.
Flushing and Skin Reactions
Some people with POTS experience episodes of facial and upper body flushing, where the skin turns red and feels hot. This is especially common in people who also have mast cell activation issues, a frequent companion condition to POTS. Researchers have described a subset of POTS patients who experience flushing alongside shortness of breath, headache, lightheadedness, and gastrointestinal symptoms. The flushing can be dramatic enough to look like a severe allergic reaction or sunburn.
POTS also frequently overlaps with hypermobile Ehlers-Danlos Syndrome, a connective tissue condition. People with both may have noticeably stretchy or unusually soft skin, joints that bend further than normal, and a tendency to bruise easily. These visible features, combined with the color changes in the legs and flushing episodes, can give clinicians important clues during a physical exam.
What Triggers Make It Worse
POTS symptoms tend to flare in predictable situations. Hot showers and baths are a common trigger because heat causes blood vessels to dilate, pulling even more blood into the extremities. Large meals can worsen symptoms because the body diverts blood to the digestive system. Dehydration, prolonged standing, and warm environments all make the visible signs more pronounced: deeper leg discoloration, more swelling, more visible distress. Many people with POTS learn to recognize these triggers and adjust their routines around them, but flares can still catch them off guard.
How POTS Is Tested
The standard clinical test is the tilt table test. You lie flat on a table that slowly tilts you to an upright angle (usually about 70 degrees) while a care team monitors your heart rate and blood pressure at regular intervals. They’re watching for that characteristic heart rate spike without a major blood pressure drop. You’ll be asked to report symptoms like dizziness, nausea, sweating, or a racing heartbeat as they occur.
There’s also a simpler version you can try at home with a blood pressure monitor, sometimes called the NASA Lean Test. After lying down for several minutes and recording your resting heart rate and blood pressure, you stand and lean your back against a wall with your heels about six inches from it. Heart rate and blood pressure are measured every minute for 10 minutes. You should try to keep your legs relaxed and avoid shifting your weight or tensing your muscles, since those movements can mask the heart rate changes. It’s important to have someone with you in case you feel faint, and to stop the test if you feel like you might pass out. This at-home test doesn’t replace a clinical evaluation, but it can give you useful data to bring to an appointment.
During the test, the key distinction clinicians look for is the absence of significant orthostatic hypotension, defined as a blood pressure drop of 20 mmHg systolic or 10 mmHg diastolic. If blood pressure drops that much, the diagnosis shifts away from POTS. The hallmark of POTS is the excessive heart rate response with blood pressure staying relatively steady.
What Day-to-Day Life Looks Like
On a practical level, POTS can look like someone who sits down a lot, lies down in unexpected places, carries a large water bottle everywhere, and wears compression stockings. Many people with POTS develop unconscious habits to manage their symptoms: crossing their legs while standing, shifting their weight, squatting suddenly in a grocery store aisle. They may seem fine at a restaurant (sitting) but struggle walking to the car afterward. The condition is often worse in the morning and can vary dramatically from day to day, which makes it look inconsistent to people who don’t understand it. Someone with POTS might be active one day and unable to get out of bed the next, not because of willpower or mood, but because their autonomic nervous system is failing to do its job.