My first reason for trying the The90 Gem UV tracker was cosmetic: I wanted to slow visible signs of aging. This The90 Gem UV tracker review, however, is about how a necklace changed my thinking about sunlight and health. The pendant, which costs $249 but was $149 at the time of publication, measures UVA and UVB separately and sends readings to a companion app. What I expected to be a vanity experiment became a lesson in how little I understood about my own exposure.
A party, a pendant, and a reality check
In August, I attended a relative’s outdoor party in Los Angeles as temperatures reached the 90s. I sat under a patio umbrella with a strong fan nearby, believing I was shielded from both heat and sun. Within half an hour I felt dizzy, nauseous, exhausted, and generally unwell — symptoms consistent with heat exhaustion. Around the same time, the Gem’s app warned that my UV exposure had risen significantly. I learned that shade does not fully block UV radiation, which can be reflected or scattered by surroundings. I had also assumed the fan and umbrella would protect me from overheating, which is a separate issue. The episode led me to discover that one of my medications increases heat sensitivity, explaining similar experiences over the years. The Gem did not diagnose anything, but it nudged me to investigate what I might otherwise have dismissed.
What the Gem measures and how it feels to wear
The sensor tracks UVA and UVB rather than relying on a local UV forecast. UVB is chiefly responsible for sunburn and helps skin make vitamin D; UVA contributes to premature aging even without a visible burn. The pendant is small and comes on a thin titanium chain in gold or silver, and I would wear it even without the tracking. Battery life lasted almost exactly the advertised week, and it recharges on an included dock. The90 plans to release a hat clip and bag tag early next year for people who prefer not to wear a necklace. The pendant detaches from the chain, which adds flexibility.
The app: useful context, uneven precision
The app is central to the experience, with clear graphs and plain-language explanations. You can create a skin profile based on skin type, sensitivities, clothing, and sunscreen so that estimates account for more than raw UV readings. Those figures are predictions, not direct measurements of how your body responds. The app estimates vitamin D production, potential circadian light benefits, nitric oxide-related benefits, cumulative UVA exposure, recent accumulated UVA exposure, and weekly trends. It also offers a Skin Aging Zone, a personalized sunburn countdown, sunscreen reminders, and a daily Sun Score. The company encourages users to aim for a Sun Score of 90, but more sun is not automatically better; too little exposure can mean missing benefits, while too much can damage skin.
In practice, the individual estimates told me more than the Sun Score. The readings responded quickly as I moved between sun, shade, and indoors, even near windows. I could not independently verify the sensor’s accuracy, but it behaved as expected in different environments. There were times it failed to register that I was outside. Eventually I learned that the app must keep running in the background on iPhone, because measurements are not stored on the sensor; fully closing the app interrupts tracking.
Surprises about vitamin D and shifting priorities
Two findings challenged my assumptions. First, the shade at that party offered far less UV protection than I had believed. Second, I accumulated very little UVB in a typical week despite living in sunny Los Angeles. I fell short of the app’s estimated sunlight-derived vitamin D target almost daily, which prompted me to look into how melanin affects vitamin D production even while offering some natural UV protection. Until then, I had mostly thought about sun exposure as a matter of preventing skin damage. Seeing how little UVB I was getting made me consider what I might be missing.
The vitamin D countdown was less helpful than I hoped. During one test, its estimate of additional sunlight needed dropped from several hours to under an hour, then climbed past six hours minutes later. The fluctuations seemed tied to changing UVB intensity, though I could not confirm that. The sunburn countdown shifted similarly. I stopped focusing on exact times and used the app for the broader : whether I was getting too much or too little sun.
Who it suits, and what I wish were better
At $249 outside a deal, the Gem is expensive, though it requires no subscription. Given how much time I spend indoors, I cannot personally justify the price, but I see the appeal for people who spend considerable time outside or want to be more mindful of sun protection. I wish the app’s guidance were clearer at times, and I wish tracking worked without the app open in the background.
My exposure often falls at one of two extremes: too little to meet the app’s estimated targets, or enough to raise concern about overexposure even when I thought shade protected me. I now try to limit outdoor time during peak UV hours and to get some sunlight on days spent mostly indoors. The Gem did not make me obsess over wrinkles; it made me pay more attention to how I treat my body.
