TattooGate: A Systematic Review of Tattoo Pigment Interference with Wearable Photoplethysmographic Sensors
DOI:
https://doi.org/10.29105/rce-fod.v21i2.184Keywords:
photoplethysmography, wearable sensors, tattoo interference, heart rate accuracy, pulse oximetry, optical sensors, signal qualityAbstract
Background: Wearable photoplethysmography (PPG) sensors are central to continuous physiological monitoring, but several factors compromise their accuracy. Tattoo pigments represent an under-characterized optical confounder that may impair heart rate (HR) and oxygen saturation (SpO₂) readings. Objective: To systematically review evidence on how tattoo characteristics, pigment composition, color, density, and anatomical location interfere with PPG signal acquisition and wearable-derived health metrics. Methods: Systematic review following PRISMA 2020 across PubMed, Web of Science, and ScienceDirect (2000–2026). Eligible studies examined the effects of tattoos on PPG signals or on the accuracy of wearable optical sensors. The risk of bias in primary studies was assessed using the JBI critical appraisal tools. Seventeen studies were included; a narrative synthesis was conducted given methodological heterogeneity. Results: Evidence was dominated by indirect sources: 10 studies (58.8%) were reviews, 4 (23.5%) experimental, and 3 (17.6%) observational. Only one study directly evaluated tattoo interference on a wearable under controlled conditions, reporting 36% complete signal dropout at rest and a 22.9% mean absolute percentage error for HR. Tattoo pigments attenuate and scatter photons in the dermal sampling volume via Beer-Lambert absorption and particulate scattering, compressing the AC pulsatile component below firmware thresholds. Spectral overlap between the ink and LED wavelengths determines the severity of interference. Conclusions: Tattoos constitute a clinically meaningful PPG confounder; signal dropout, not algorithmic bias, is the dominant failure mode. SpO₂ accuracy in tattooed individuals remains understudied, and direct empirical evidence is scarce, so generalization must be cautious. Future research should standardize tattoo characterization, ensure diverse and adequately powered samples, assess multiple metrics, and develop algorithmic and hardware mitigation.
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