Yes, nail polish can change the reading on a fingertip pulse oximeter, and the color matters. In the studies, the trouble came mostly from dark shades like black, blue, green or brown. With most polish on a healthy person, the error was small, often under one point. But not always: some dark nails gave no reading at all, and gel polish pushed one oximeter’s number up, which is the more worrying direction. The fix is simple. Take the polish off the one finger you measure on, just as the FDA says.
I’m not a doctor, a nurse or a pharmacist, and this isn’t medical advice. If your doctor gave you an oxygen number to watch, their instructions come first, and a reading that worries you is always worth a call.
Why Polish Gets in the Way of the Light
A fingertip oximeter shines light through your finger and measures what comes out the other side. It uses two kinds: red light and infrared light. Blood that’s carrying oxygen soaks up those two differently than blood that isn’t, and the oximeter works out your oxygen level from that difference, beat by beat.
Your nail sits right in the path of that light. Clear, bare nail lets it through. A coat of polish can soak some of it up, and here’s the catch: it may not soak up both kinds equally. A 1988 study in Anesthesia & Analgesia measured exactly that. The oximeter it tested used light at 660 and 940 nanometers, and the colors that threw the reading off the most were the ones that absorbed those two very differently.
So it isn’t about how dark a polish looks to you. It’s about how it looks to the oximeter (and an oximeter doesn’t see color the way we do). That’s also why the results jump around from one study to the next. Different devices use slightly different light, and different brands of the “same” color aren’t made the same way.
Which Colors Caused Trouble in the Studies
That 1988 study, led by Charles Coté, painted the nails of 14 adult volunteers in five colors (blue, green, purple, black, red). Blue and green lowered the reading the most. Black came next, and purple and red lowered it less. The team also predicted from the lab data that a brown-red shade would interfere, then tested it, and it did.
A 2013 study in Nigeria tried four colors plus an acrylic nail on 50 volunteers, using a low-cost oximeter called the Lifebox. Clear polish, red polish and the acrylic nail made no real difference. Dark polish was another story. Only 12% of the nails painted black gave any reading at all, and only 64% of the brown ones did. When they did read, the numbers came out lower.
That “no reading” result matters. An oximeter that just blinks or shows dashes on a painted finger isn’t broken. It may simply not be getting enough light through the polish.
How Big the Error Usually Is
The newer studies are more reassuring, honestly. Most found the error smaller than people fear. In 2007, researchers in South Carolina tested 10 colors on 27 healthy volunteers with two hospital oximeters. Brown and blue lowered the reading on both machines, but by less than one point, which they called not clinically significant.
A German team checked nine colors on 50 patients in intensive care the same year, comparing the oximeter against a blood test. Black made the biggest gap, an average of 1.6 points too low. Purple came next at 1.2 and dark blue at 1.1. Every other color, clear included, ran 0.2 to 0.9 points low. All of that sat inside the plus or minus 2 points the device makers list in the fine print.
Now put that next to the error every oximeter carries anyway. The FDA has said that when an oximeter it cleared reads 90%, your true oxygen level is generally somewhere between 86% and 94%. Many over-the-counter oximeters sold for “wellness” or sports never go through FDA review at all. So polish adds its own error on top of an error band you already have. A point or two can matter when the reading is already close to the number your doctor told you to watch.
Read more: Pulse Oximeter Readings Chart Explained: From 95% to 100%
Gel Polish Can Read High, and That’s the Worse Mistake
Gel manicures last for weeks, and taking one off takes a special process, not a quick swipe of remover. A 2019 study from Singapore looked at exactly that, testing 10 gel colors on 17 healthy women with two different oximeters.
On one oximeter, light blue and orange gel pushed the reading up, by about one point for light blue. On the other, the numbers got shaky. Compared with the same nails bare, its readings could swing by up to 2 points on pink and as much as 17 points on black.
A high reading is the worse mistake, for a simple reason. A number that’s too low makes you double-check. A number that’s too high can make you relax when your oxygen is actually dropping. The authors said the same thing: gel can make the display read higher than your true level, which can delay noticing low oxygen. Their advice was to remove the gel or measure another way.
Acrylic Nails and Press-Ons
Artificial nails add a thick layer the light has to pass through, polished or not. The evidence here is mixed, honestly. That Nigerian study found an unpainted acrylic nail made no real difference on its oximeter.
The German team ran a separate test on acrylic nails in 2007, again in intensive care patients and against a blood test. With one brand of oximeter, the acrylic nail read 1.1 points low on average, a real difference. With the other brand, it read 0.8 points high, and that one wasn’t significant. Same kind of nail, two machines, two answers.
That’s the frustrating part for anyone at home. You can’t know which way your own device leans, and I don’t love guessing with an oxygen number. If you wear acrylics and check your oxygen often, I’d keep one nail natural, the one you clip the oximeter on.
Turning the Clip Sideways: Does It Help?
You may have heard this trick: if you can’t take the polish off, turn the oximeter sideways so the light goes through the sides of your finger instead of through the nail. It’s been tested in hospitals, too.
It helped some, but it didn’t solve the problem. In the German intensive care study, turning the sensor 90 degrees cut the average error from 2.8 points to 1.3 in the 10 patients they tested it on, and that drop wasn’t statistically significant. The authors wrote plainly that rotating the sensor doesn’t get rid of the error. The South Carolina team tried the side-to-side setup too, and one of their machines still read a little low with red polish.
Also, a fingertip clip at home isn’t built to sit sideways. It can slip, and a sensor that’s half on the finger gives a jumpy reading of its own. Check the manual for your model. If it doesn’t mention sideways use, I wouldn’t count on it.
The Easy Fix: One Bare Finger
You don’t have to give up your manicure. You just need one finger the light can read cleanly. The FDA’s advice for home oximeters starts right there: remove any fingernail polish on the finger you measure. If you get gel or acrylic nails and check every day, you could ask the salon to leave that one nail bare.
The rest of the FDA’s routine is just as plain. Make sure your hand is warm and relaxed, held below the level of your heart (cold hands throw the reading off, too). Sit still. Wait until the display stops changing and shows one steady number, then write it down with the date and time.
Use the same finger every time, too, so your log compares like with like. The FDA says to watch the trend over time, not one single reading.
Read more: Perfusion Index on a Pulse Oximeter: What the PI Number Means
When the Number Means Call Your Doctor
A polished nail hides one more thing people forget. The FDA lists bluish color in the face, lips or nails as a sign of low oxygen. Under a coat of navy polish, you won’t see your nails change color. So look at your lips and face as well, and don’t lean on the display alone.
The FDA’s other warning signs are shortness of breath or a worsening cough, restlessness, chest pain or tightness, and a fast or racing pulse. Some people with low oxygen have none of these, which is exactly why the trend matters. Call your doctor if your oxygen stays lower than your usual, or lower than the number they gave you, after you’ve warmed up and rechecked on a bare finger.
If you have trouble breathing, chest pain that won’t go away, or lips or skin that look gray or blue, don’t wait for any device. Call 911. If you live alone, call someone.
The Short Version
Nail polish can change the reading. Dark colors did it most in the studies, gel can push the number up, and acrylic nails depend on the device. On a healthy person the error is often small, but it adds to the error your oximeter already has. The fix costs you one finger: take the polish off it, warm your hand, sit still and wait for a steady number.
If you have darker skin, there’s a separate accuracy question the FDA is still working on, and it has a guide of its own here. And if you have a question about your own oximeter, leave it in the comments. I read every one.
Read more: Best Pulse Oximeter for Dark Skin
