Weather 
My approach to sunscreen has long been simple: If I’m not pink yet, I’ve got time.
As a wellness reporter who writes about skin health, I know better. I know the sunscreen rules. I know the risks. I know that “I’ll just put more on later” is not exactly a sound dermatological strategy.
And yet, every summer, I somehow fall into the same trap. I stay in the sun a little too long, forget to reapply and end up spending the night marinating in aloe.
But this year, I’ve had something calling my bluff — before I can get burned. It’s called The90 Gem, a smart necklace that tracks real-time exposure to ultraviolet (UV) light and adjusts its personalized sun-care guidance as conditions change throughout the day.
Priced at $299, the device comes in gold or silver and, in my case, easily passed as just another accessory.
“I love how wearable technology can make you more connected with your body,” Stacy Salvi, co-founder and CEO of The90, told The Post. “But I wanted to have something that women could wear as jewelry that nobody would guess is a tracker.”
Beyond the burn
The Gem’s lightweight tech is tucked inside a black charm, where an advanced sensor measures both UVA rays — which contribute to skin aging, including fine lines, wrinkles and hyperpigmentation — and UVB rays, which are the primary cause of sunburns. (Both contribute to skin cancer.)
Over time, exposure to both types of UV radiation can increase the risk of melanoma and other skin cancers.
“Even without an immediate reaction like a sunburn or tan, the effects of both UVB and UVA are still reaching the skin, impacting the skin at the cellular and molecular level that may not be clinically visible,” said Dr. Helen He, co-director of Mount Sinai-Clinique Healthy Skin Dermatology Center, who is not affiliated with The90.
“These cellular and molecular changes do not develop overnight, but instead accumulate in the skin over years of chronic sun exposure, leading to significantly increased risk of both skin cancer and accelerated skin aging,” she explained.
The Gem, at least in theory, could help me catch some of that invisible exposure in real time.
Keeping score in the sun
Getting started is fairly simple. On the companion app, I answered questions about my skin type, hair and eye color, family history, and whether I take medications or have medical conditions that could increase my sensitivity to UV radiation.
It also asked about my sunscreen habits — how often I wear it, what kinds I use and whether I’m a “sun seeker” or “sun avoider.”
The app then combined my personal profile with the Gem’s UV readings to provide live estimates of my risk of burning and skin aging.
One morning, while working outside, my phone told me the UV index — a standard scale from 0 to 11+ that measures the strength of UV radiation at a given place and time — was a 2.
“[That’s] low, meaning it’s a great time to spend outdoors,” the app said. “The UV index is expected to reach 8 between 12pm and 3pm, and, at that level, you could burn in just 37 minutes without protection.”
But as the temperature climbed and the UV grew more intense, I checked the app again. A countdown was ticking away, showing how long I had before I was likely to start burning.
There were just two minutes left.
Shortly after, my phone buzzed with a reminder to reapply my sunscreen — which I actually did, despite having zero visible signs of a burn.
“Enjoy the sunshine, but be mindful of your skin,” the app said. “Consider applying protection or seeking shade if you intend to stay longer.”
I probably would have dismissed the same advice as nagging if it came from a loved one. But for some reason, coming from my phone, I listened.
On another blazing-hot afternoon, the app nudged me to cover up outside, so I retreated to my apartment and settled into my favorite window nook to read.
Later, I saw in the app that my “Skin Aging Zone” was still showing UV stress. Turns out, coming inside didn’t mean I’d escaped the sun entirely. While my UVB exposure had dropped, UVA rays can penetrate glass — including car and airplane windows — and continue to damage the skin.
The app also caught me off guard on an overcast day, when it alerted me that my skin-aging risk was elevated. Clouds don’t block all UVA radiation, so you can still be exposed when it’s gloomy outside.
“[Your] weather app hasn’t been telling you the whole story,” said Salvi, the daughter of a dermatologist and longtime wearables expert who spent more than eight years at Fitbit.
“Protecting against sunburns is definitely very important, so we try to help with that, but it’s really the UVA measurement that’s lacking,” she explained. “The UV index doesn’t really tell you anything about it.”
It’s not all bad news
The Gem isn’t just focused on the risks of UV exposure.
It also tracks how much vitamin D you’re getting from the sun and estimates how much longer you should spend outside to reach the recommended daily dose.
That’s important because vitamin D plays a vital role in helping build and maintain strong bones. It also contributes to immune function, muscle health and communication between the brain and body.
And most people aren’t getting enough of it. In the US, about 42% of adults are vitamin D deficient, with rates even higher among people with dark skin.
The goal, Salvi said, isn’t to convince people to hide from the sun altogether. It’s to find a balance between protecting your skin and getting the benefits of spending time outdoors.
Keeping track of the trackers
The90 designed the Gem with women in mind, but the company plans to eventually offer versions better suited for men and children.
For me, the necklace was a plus. My wrist is already occupied by a smartwatch, while an Oura ring has claimed my finger. And unlike other wearables I’ve used, no one guessed the Gem was a tracker.
But I found myself wishing it could do more. The Gem’s insights were genuinely useful, and its alerts actually changed my behavior. Still, it meant adding another device to the growing collection already tracking my body — one more thing to wear, charge and keep tabs on throughout the day.
Give me a gadget that can measure my UV exposure alongside the other biometrics I care about and pull it all into one app, and I’d buy it in a heartbeat.
In the meantime, at least The90 doesn’t make me pay for another monthly subscription. That’s something I can’t say for any of the other smart devices I use.
And if the Gem can keep me from turning into a raisin in the sun — or, more importantly, encourage me to take the precautions I have a tendency neglect that could lower my skin cancer risk — I’d say it’s earned its place around my neck.
