INTRODUCTION: Pulse oximetry is the standard monitoring technique of functional oxygen saturation (SpO). As the use of fingernail polish has been described to alter SpO readings, its removal is commonly recommended prior to measurement. Gel-based manicures have gained popularity in recent years due to their attractiveness and longevity. However, the removal of gel nail polish requires a specialised procedure. Valuable time and resources can be saved if removal can be avoided. To our knowledge, there are no available studies on the effect of gel-based manicures on pulse oximetry readings. Hence, we evaluated the effect with two oximeters, using different technology and wavelength combinations. METHODS: 17 healthy female adult volunteers were recruited for this single-blind randomised controlled trial. Subjects with hypothermia, hypotension, poor plethysmographic waveform and nail pathology were excluded. Colours tested were: black, purple, navy blue, green, light blue, white, yellow, orange, pink and red. Pulse oximetry was measured at 15- and 30-second intervals using two different pulse oximeters, the Philips M1191BL and Masimo SET®. Means were compared using paired t-tests. RESULTS: Using the Masimo oximeter, light blue (ΔM = 0.97% ± 0.96%; p = 0.001) and orange (ΔM = 0.76 ± 1.17%; p = 0.016) gel nail polish resulted in a statistically significant increase from baseline SpO readings. With the Philips oximeter, the limits of agreement ranged from 2% for pink to 17% for black, indicating imprecision. CONCLUSION Gel-based manicures can result in overestimations of actual readings, delaying detection of hypoxaemia. Gel nail polish should be routinely removed or an alternative monitoring technique sought.