Skip to content
Decision-ready map
• Program risk: confounders cause unequal “unable-to-measure” and misclassification
• Procurement: require interference testing matrix + clear labeling/alternatives
• Training: site check + relocation workflow + mismatch escalation
• Monitoring: capture confounder context (polish/tattoo/cosmetics/scar) in incident logs
• Equity: offer alternatives instead of excluding participants
(1) What it is
In scaled deployments, surface confounders (hair, tattoos, scars, cosmetics) can drive systematic ‘unable-to-measure’ events and misclassification in PPG/SpO₂, spectroscopy, and NIRS. Theme 6 asks programs to design procurement, training, and referral pathways that treat confounders as expected conditions—not exceptions—so that safety and inclusion hold at scale.
(2) Who it helps
Organizations procuring devices, running community screening or home-monitoring programs, training staff, and publishing public guidance.
(3) What evidence exists
Nail polish interference is synthesized in a systematic review; dye interference is documented perioperatively; scar DRS studies show altered optical properties; cosmetics and tattoo pigments have measurable optical signatures; standards and reference datasets exist for reflectance baselines and device performance expectations.
(4) Translation barriers
Commodity procurement without interference evidence; training that over-relies on thresholds; lack of alternative-site workflows; missing incident logging for confounders; field conditions (motion, lighting) interact with surface layers.
(5) Equity/safety checks
Confounders correlate with culture, occupation, and identity (tattoos/cosmetics), and injury history (scars). Programs should offer alternatives rather than exclusions and use non-stigmatizing messaging.
(6) Decision questions
• Do procurement specs require interference evidence and clear labeling/alternatives?
• Are staff trained to inspect/relocate and use mismatch escalation?
• Are confounder contexts captured in incident logs?
• Do protocols avoid single-threshold rules when quality is low?
• Are equity impacts monitored (higher failure rates in certain groups)?
(7) Practical next steps
1) Add interference evidence and labeling requirements to procurement.
2) Train a simple workflow: inspect → relocate → quality gate → escalate if mismatch.
3) Provide alternative sites and scripts for non-stigmatizing guidance.
4) Monitor failure rates and incidents with confounder context.
5) Publish transparent limitations and referral pathways.
(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
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
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
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