The science of The90
The science your weather app and sunscreen have been wrong about.
Your weather app reports one number for a whole city. Your sunscreen can’t tell you when it has worn off. The90 measures the UV your skin actually receives, then translates the peer-reviewed science into plain language so you can decide for yourself.
of visible skin aging is caused by UV.¹
Aging is not destiny. Genetics and time set a floor. Everything else (fine lines, sun spots, sagging, uneven tone) is shaped by what your skin experiences. And the single largest input is ultraviolet light, most of which you can’t feel.
Two rays. Two completely different jobs.
Most consumer sun products lump them together. Your skin doesn’t. Neither do we.
UVB · The burning ray
Shorter wavelength. Higher energy. Affects the top layers of skin. Responsible for sunburn, erythema, and a significant share of skin cancer risk. You can feel it.
UVA · The aging ray
Longer wavelength. Penetrates deeper into the dermis. Breaks down collagen and elastin. Responsible for wrinkles, sagging, sun spots. You don’t feel it. It penetrates clouds and glass. 95% of the UV reaching the ground.
The UV Index is from 1994.
A useful standard for its time. An incomplete picture for ours.
1. It’s a zip-code estimate.
Calculated for a flat, open area on a clear day. It can’t see the snow at your feet, the water beside you, the glass of your car, the concrete bouncing light back.
2. It’s weighted toward UVB.
Built around erythema (sunburn risk). UVA is systematically underrepresented. A single UVI number can read “moderate” while your aging exposure is anything but.
Your skin, in one number.
The Sun Score is your personal exposure score. It’s calculated from live UVA and UVB readings, your skin profile, and your habits.
Live UVA and UVB intensity (from The Gem, every few seconds)
Your Skin Profile ID (Fitzpatrick type, sensitivity, sun history)
Your sunscreen status (logged in-app)
Your behavior over time (the app learns)
Sun Score
Personalized to your skin, today
Avoiding the sun isn’t the goal. Knowing your dose is.
Sunlight regulates your circadian rhythm, supports vitamin D synthesis, modulates mood and metabolic health, and is central to hormone signaling. The goal is the right dose for your body. Not zero.
Built with the people who study this for a living.
Advisor 2 · Add as confirmed
Research citations.
1. Flament, F. et al. (2013). Effect of the sun on visible clinical signs of aging in Caucasian skin. Clinical, Cosmetic and Investigational Dermatology. DOI: 10.2147/CCID.S44686
2. Citation 2 placeholder · Journal · Authors · Year · DOI link.
3. Citation 3 placeholder · Journal · Authors · Year · DOI link.
The90 Gem is not a medical device. It is intended for informational and educational use only and is not designed to diagnose, treat, cure, or prevent any disease. The Gem does not replace sunscreen or medical advice. Always follow guidance from your dermatologist or physician.
Is there a subscription or monthly fee?
No. Your Gem comes with the full The90 app and every core feature, with no monthly fee to read your own light. You buy the sensor once.
What does The Gem actually measure?
It reads the UVA and UVB reaching your skin, separately and in real time, then turns the day into a single Sun Score from 0 to 100. Along the way it tracks the light you want, like your morning circadian light and your estimated vitamin D, and the exposure you want to manage, like the UVA that ages your skin.
Do I have to wear it as a necklace?
It comes as a jewelry-grade pendant on a matching gold or silver chain, so you can wear it out of the box. The Gem is also a removable core, so it can move into new ways to wear it as they launch, including a hat clip and bag tag on the way.
How is this different from the UV Index or my weather app?
The UV Index gives one number for a whole city and says the same thing to everyone. The Gem measures the light actually hitting your skin, separates the aging rays from the higher-energy ones, and reads it against your personal skin profile in real time. It is the difference between a forecast and your actual day
Can I wear it in the water?
Rain, sweat, and a quick rinse are all fine. The Gem is water resistant to 1 meter for 30 minutes, so leave it off for the pool, the shower, hot tubs, and saunas.
What if it is not for me?
Try it for 30 days. If it is not right, send it back for a full refund, and every Gem is covered by a 1-year warranty. Free shipping, dispatched from California within 1 to 2 business days, currently within the US.
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