We think it’s pretty cool.
Samsung’s Galaxy Watch 8 can already track your heart rate, sleep, and workouts. But that apparently isn’t enough information about you. Its antioxidant index turns a five-second thumb scan into a score from 0 to 100.
The watch does not measure all the antioxidants in your body. Instead, it estimates carotenoids, pigments with antioxidant properties found in yellow, orange and green fruits and vegetables that can build up in your skin. Samsung uses this reading as an indicator of fruit and vegetable consumption, although the company says UV exposure, alcohol and stress can also affect the score.
How the sensor reads your skin
To take a measurement, remove the Galaxy Watch 8, open Samsung Health on the watch, select Antioxidant Index and tap Measure before pressing your thumb against the BioActive sensor on the back. Samsung says the sensor uses multi-wavelength absorption spectroscopy to analyze how different wavelengths of light are absorbed and reflected by the skin.
It’s much more dramatic than pressing your thumb to a smartwatch. In practice, the sensor uses yellow, blue, purple and green LED light to illuminate your skin; carotenoids absorb certain wavelengths more strongly (blue is most important here) and photodiodes detect reflected light, allowing Samsung to estimate carotenoid concentration and calculate an antioxidant index.
The thumb was not selected simply because it fits the sensor well. Melanin and hemoglobin can interfere with optical measurements, Samsung explains, so the skin on the fingers helps minimize interference from melanin while pressure from your thumb temporarily restricts blood flow, reducing interference from hemoglobin.
How accurate is the Galaxy Watch 8 Antioxidant Index?
Samsung says it validated its sensor using Raman spectroscopy, a laboratory technique used to measure skin carotenoids, and compared the results with blood tests, food diaries and clinical data from several hundred participants. Separately, a 2023 randomized controlled trial involving Samsung researchers also found a strong correlation between reflection spectroscopy and Raman spectroscopy when measuring skin carotenoids.
But there is one big caveat. Samsung has not released a simple consumer-facing accuracy percentage or margin of error for the Galaxy Watch 8 feature, and it states that the Antioxidant Index is not intended to diagnose or treat medical conditions. Think of the score as another health trend to monitor, rather than a blood test packed into a little computer on your wrist.
This number may be stubborn, according to Woozad’s Galaxy Watch 8 review. After Amy Skorheim deliberately changed her diet for one day, her score dropped two points. The following days, his readings varied between 56 and 60.
Samsung’s current US comparison chart does not list the Antioxidant Index for the Galaxy Watch 7. It lists features for the Galaxy Watch 8, Watch 8 Classic, and Galaxy Watch Ultra (as well as the new Watch 9 and Ultra2), but Samsung hasn’t specified why the Watch 7 is lacking. The company says it typically takes two to three weeks for carotenoids in foods to build up in the skin to detectable levels.
