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Decision-ready map
• Tell the study team if you have nail polish/gel, tattoos, scars, or makeup at the site
• If readings seem off: remove cosmetics when possible or use a different site
• Numbers are estimates; symptoms matter more than a single reading
• Ask what the device does when the signal is low-quality
• Ask how results will be reported and what labels/limits apply
(1) What it is
Biophotonic devices use light to estimate oxygen levels (SpO₂/NIRS), pulse patterns (PPG), or tissue composition (spectroscopy). Hair, tattoos, scars, and cosmetics can change what the device ‘sees’ by blocking, absorbing, or scattering light before it reaches blood or tissue. That can make readings less reliable or cause the device to fail to get a reading. This brief explains what to tell the study team, what questions to ask, and what safe alternatives should exist.
(2) Who it helps
This brief is for patients and community members in studies or monitoring programs using wearable PPG/SpO₂, tissue spectroscopy (DRS/fluorescence/Raman), or NIRS/tissue oximetry—especially if readings may influence when to seek care or how the research data are interpreted.
(3) What evidence exists
Research shows some cosmetics and pigments can affect readings. A 2023 systematic review found that some nail polish colors can slightly reduce SpO₂ or occasionally prevent measurement. Surgical dyes can cause ‘false low’ oxygen readings in the operating room even when true oxygen is fine. Scar tissue has different optical properties: studies using diffuse reflectance spectroscopy in keloid scars show measurable differences in collagen/water and scattering/oxygenation estimates compared with normal skin. Cosmetics like foundation measurably change skin reflectance and absorbance, and reflectance spectroscopy is used to study skin reactions to topical products. Tattoo inks have distinct chemical signatures detectable by Raman spectroscopy, meaning tattoos can change spectral measurements unless accounted for.
(4) Translation barriers
In real life, it can be hard to notice confounders: clear gel polish may look like bare nails; tattoos may be under wearable sensors; makeup or lotion may be applied automatically. Some programs don’t explain what to do if the device can’t read or if the number seems wrong.
(5) Equity/safety checks
Fair research should work for everyone. Studies should not exclude participants because of tattoos, scars, or cultural cosmetics; instead they should provide alternative sites and document conditions. Your privacy matters: if a study records tattoos or cosmetic use, it should explain why and how the information is protected.
(6) Decision questions
• Was the device tested with common confounders (nail polish/gel, tattoos, scars, cosmetics) and what does it do if the signal is poor?
• If I have tattoos/scars or I wear cosmetics, where should the sensor go instead?
• What should I do if the reading looks wrong or if symptoms disagree with the number?
• Will my results be interpreted with these conditions documented, and how is privacy protected?
• Who do I contact if the device repeatedly fails to get a reading?
(7) Practical next steps
1) Tell the study team if you have nail polish/gel, tattoos, scars, or cosmetics where the sensor sits.
2) If possible, remove cosmetics at the measurement site or use a different site (toe/earlobe/alternate location) as instructed.
3) Follow the mismatch rule: symptoms matter more than a single number; seek advice if you feel worse even if readings look normal.
4) Ask for a plain-language sheet explaining device limits, quality flags, and what happens when readings are unreliable.
5) Report repeated failures so researchers can improve labeling, placement guidance, and device design.
(8) References
Aggarwal AN, Agarwal R, Dhooria S, et al. Impact of Fingernail Polish on Pulse Oximetry Measurements: A Systematic Review. Respiratory Care. 2023.
https://doi.org/10.4187/respcare.10399
Yeganehkhah M, Dadkhahtehrani T, Bagheri AR, Kachoie A. Effect of Glittered Nail Polish on Pulse Oximetry Measurements in Healthy Subjects. Iran J Nurs Midwifery Res. 2019.
https://doi.org/10.4103/ijnmr.IJNMR_176_17
Hueter L, Schwarzkopf K, Karzai W. Interference of patent blue V dye with pulse oximetry and co-oximetry. Eur J Anaesthesiol. 2005.
https://doi.org/10.1017/S0265021505230818
Howard JD, Moo V, Sivalingam P. Anaphylaxis and other adverse reactions to blue dyes: a case series. Anaesth Intensive Care. 2011.
https://doi.org/10.1177/0310057X1103900221
Piñero A, Illana J, García-Palenciano C, et al. Effect on Oximetry of Dyes Used for Sentinel Lymph Node Biopsy. Arch Surg. 2004.
https://doi.org/10.1001/archsurg.139.11.1204
Poon KWC, Dadour IR, McKinley AJ. In situ chemical analysis of modern organic tattooing inks by micro-Raman spectroscopy. J Raman Spectrosc. 2008.
https://doi.org/10.1002/jrs.1973
Sadura F, Wróbel MS, Karpienko K. Colored Tattoo Ink Screening Method with Optical Tissue Phantoms and Raman Spectroscopy. Materials (Basel). 2021.
https://doi.org/10.3390/ma14123147
Hsu C-K, Tzeng S-Y, Yang C-C, et al. Non-invasive evaluation of therapeutic response in keloid scar using diffuse reflectance spectroscopy. Biomed Opt Express. 2015.
https://doi.org/10.1364/BOE.6.000390
Tseng S-H, Hsu C-K, Lee JY-Y, et al. Noninvasive evaluation of collagen and hemoglobin in keloid scars using DRS. J Biomed Opt. 2012.
https://doi.org/10.1117/1.JBO.17.7.077005
Yoshida K, Okiyama N. Estimation of reflectance/transmittance/absorbance of cosmetic foundation layer on skin. Opt Express. 2021.
https://doi.org/10.1364/oe.442219
Mancuso A, d’Avanzo ND, Cristiano MC, Paolino D. Reflectance spectroscopy to explore skin reactions to topical products. Front Chem. 2024.
https://doi.org/10.3389/fchem.2024.1422616
Kim KB, Baek HJ. Photoplethysmography in Wearable Devices: A Comprehensive Review. Electronics. 2023.
https://doi.org/10.3390/electronics12132923
Cooksey CC, Allen DW, Tsai BK. Reference Data Set of Human Skin Reflectance. J Res Natl Inst Stan. 2017.
https://doi.org/10.6028/jres.122.026
Cooksey CC, Allen DW, Tsai BK. Reference Data Set of Human Skin Reflectance (data). NIST. 2017.
https://doi.org/10.18434/M38597
IEC. ISO 80601-2-61:2026 Pulse oximeter equipment — safety and essential performance.
https://webstore.iec.ch/en/publication/74527