Gem’s UV tracking made one wearer rethink how sunlight affects health beyond appearance

A warning in the shade

At an outdoor family party in Los Angeles, where August temperatures reached the 90s, the wearer sat under a patio umbrella with a fan nearby. About half an hour later, they felt exhausted, dizzy and nauseous, symptoms consistent with heat exhaustion.

Around the same time, the Gem app sent an alert that UV exposure had climbed considerably. The wearer realized the umbrella had not blocked all radiation, which can be reflected or scattered by surrounding objects. Shade and a fan had also been mistakenly assumed to protect against both UV exposure and overheating.

The episode prompted the wearer to look into similar past experiences. They discovered that one of their medications increases heat sensitivity. The Gem did not diagnose the cause, but the alert helped prompt further investigation.

A shift in priorities

The wearer had first been interested in tracking UV mainly to limit visible signs of aging. They said their Indian heritage and higher melanin content meant they rarely got sunburned, but that does not remove the risk of sun damage or skin cancer. Living near the beach in sunny Los Angeles also meant they had not paid much attention to their UV exposure.

Since the episode, they have tried to limit time outdoors during peak heat and UV hours, stay hydrated and monitor how they feel outside. The experience broadened their interest in the device beyond appearance and skin aging.

What the pendant measures

Gem’s sensor measures UVA and UVB separately rather than showing only the local UV forecast. UVB is chiefly responsible for sunburn and helps the body produce vitamin D; UVA contributes to premature aging, even without visible burning.

The pendant is circular and comes with a thin necklace and a titanium chain in gold- or silver-colored finishes. Its battery lasted almost exactly a week, matching the advertised lifespan, and it recharges on an included dock. The90 planned to release a hat clip and bag tag early the following year.

App estimates and limits

The app presents graphs and plain-language explanations. Users can create a skin profile using factors including skin type, sensitivities, clothing and sunscreen. Its estimates therefore draw on more than UV readings alone.

The app includes estimated vitamin D production, possible circadian light and nitric oxide-related benefits, and cumulative UVA readings. Its Skin Aging Zone assesses potential aging-related risk. These figures are predictions, not direct measurements of how an individual’s body responds to sunlight.