Why hospitals ask you to remove gel nails: colour and fingertip oxygen meters
Fingertip oxygen meters shine light through the nail, and some gel colours skew them. What a 2019 trial and a review found, and how to prepare before hospital.
- A fingertip oxygen meter shines light through the nail. Opaque or dark colour can block some of it and skew the reading.
- A 2019 trial found some gel colours raised readings by about 1%, and one device was imprecise with dark colours.
- Reviews say the effect is mostly small, within the device's ±2% accuracy, but always follow the hospital's instructions.
- Before surgery, remove gel ahead of time the proper way, and tell the nurse if any is left.
Before surgery or a hospital stay, many hospitals ask you to remove nail polish and gel. The main reason is the fingertip oxygen meter (pulse oximeter), which works by shining light through the nail. Opaque or dark colour can skew the reading. Research says the effect is usually small, but in an operating room a small error can mean a problem is noticed later. This article explains what happens and how to prepare your nails.
How a fingertip oxygen meter works
The meter has a light source on one side and a sensor on the other, clipped onto your fingertip. The light has to pass through the nail, the tissue under it and the blood, and the device then works out what percentage of your blood is carrying oxygen. That number is called SpO2.
If a layer of colour is in the way, some of the light is absorbed before it reaches the blood, and the device may calculate wrongly. Gel is harder to remove than regular polish: it takes soaking and time, which is awkward on the day. That is why surgical teams care about it.
What the 2019 trial found
Anaesthetists at a hospital in Singapore ran a randomised trial with 17 healthy female volunteers. They tested 10 gel colours: black, purple, navy blue, green, light blue, white, yellow, orange, pink and red, using two oximeters built on different technology.
- First device: light blue gel raised readings from baseline by an average of 0.97%, and orange by 0.76%. Both were statistically significant.
- Second device: the limits of agreement ranged from 2% for pink to 17% for black, meaning the readings were imprecise.
The authors concluded that gel can make readings higher than reality, which may delay spotting low oxygen. They recommended removing gel routinely or using another way of monitoring.
An overestimate is the worrying direction: the number on the screen looks normal while real oxygen may be starting to drop.
What other sources say
The findings do not all point the same way.
| Source | Finding |
|---|---|
| Systematic review, 2015 (Spain) | 12 trials. All but 2 found at least one colour lowered SpO2 significantly, but within the ±2% error of the devices. Authors judged it not clinically significant |
| Gel trial, 2019 (Singapore) | Some gel colours raised readings by about 1%. One device was very imprecise with dark colours |
| Open Critical Care | Blue, green, black, purple and brown polish interfere most, with up to 3-5% underestimation, though data are mixed |
| UK Safe Anaesthesia Liaison Group (SALG), 2023 | Judged that keeping acetone remover in anaesthetic rooms (risk of the wrong bottle being given to a patient) is a bigger risk than polish interfering with readings |
In short: for most healthy people the effect of nail colour is small, but devices respond differently and dark colours skew more. Hospitals choose to remove it first, because it is an easy variable to take out.
Worked example: a 1% shift against a ±2% error
Made-up numbers to picture it, not medical thresholds.
- Say the real oxygen level is 93%.
- With the device’s normal ±2% error, the reading could already be anywhere from 91% to 95%.
- If a gel colour adds about 1% on average (like light blue in the trial), that window moves to roughly 92% to 96%.
- With a device whose limits reach 17% on black, the number on screen is barely usable.
Step 3 is why reviews call the effect small. Step 4 is why surgical teams do not want to take the chance.
How to prepare your nails before hospital
- Read your pre-op instructions or phone to ask. Rules differ between hospitals, and some may ask for both hands and feet.
- Remove gel ahead of time, not on the morning of surgery. Soak it off as in removing gel safely. Do not peel.
- If you could not remove it, tell the nurse. They may clip the probe sideways on the fingertip or use a toe, options listed by Open Critical Care.
- Do not reapply during your stay. Ask your doctor if you are not sure when it is fine to do your nails again.
- Look after your nails meanwhile. They may be thin for a while after removal. See nail care after gel.
Common mistakes
- Peeling gel off the night before surgery. Layers of nail come off with it, leaving the nail thin and sore. Plan removal ahead.
- Assuming pale gel is fine. In the trial, the colours that significantly shifted one device were light blue and orange, not only dark shades.
- Clearing your hands but forgetting your feet. Toes are sometimes used for monitoring. Ask whether toenails need clearing too.
- Not telling staff you still have gel. Telling them helps them choose a good place to measure.
- Measuring at home on a painted finger and then panicking or relaxing over the number. If your doctor asked you to monitor, use an unpainted finger.
This article is general information. If your hospital or doctor tells you something different, follow them.
The next article in this series looks at the 2023 study on nail lamps and cell DNA.
Sources
- The effects of gel-based manicure on pulse oximetry — Singapore Medical Journal 2019 (via QxMD)
- Influence of nail polish on pulse oximeter readings of oxygen saturation: a systematic review — Emergencias 2015 (PubMed)
- Does nail polish impact pulse oximeter accuracy? — Open Critical Care
- Acetone in the anaesthetic room: time for a change — Safe Anaesthesia Liaison Group
FAQ
Do I need to remove gel from every finger, or is one enough?
It depends on the hospital. Some ask for every nail, some for only a few. Follow your pre-op instructions or ask the nurse. Without clear instructions, removing all of it is the safest choice.
What if I end up in the emergency room with gel on?
Tell the staff you have gel. They have ways around it, such as clipping the probe sideways on the fingertip, using a toe, or another test if needed. Do not peel the gel off yourself.
Does the same apply to an oximeter at home?
Same principle: nail colour changes how light passes through. If your doctor asked you to monitor readings, use a finger with no polish, and ask your doctor what to do if readings seem unreliable.
General guidance. Products differ between brands: always follow the label. If you react to a product, see a doctor.