What the UV Index Actually Means

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We get sunlight each day, but immoderate days the ultraviolet rays are stronger than others. You cognize this intuitively if you’re prone to burning: You astir apt skip the sunscreen if you’re going for a locomotion successful the winter, but slather it connected for a midday summertime hike. The UV scale is simply a mode of putting a fig connected however beardown the sun’s rays are, alternatively than relying connected a gut feeling.

What is the UV index?

The UV scale measures ultraviolet (UV) radiation from the prima astatine the level of the Earth’s surface, and is meant arsenic an indicator of the imaginable for prima harm connected our skin.

Ultraviolet radiation, and frankincense UV scale numbers, are higher erstwhile the prima is astatine a higher space successful the sky. Outside of the tropics, this means the UV scale is highest during midday successful the summer. (The space of the prima successful wintertime is shallower, adjacent successful the mediate of the day.)

Other factors include:

  • Altitude (UV is stronger astatine higher altitude)
  • Cloud screen (the thinner the clouds, the much UV penetrates)
  • Latitude (the further you are from the equator, the little UV reaches the earth)
  • Ozone (which tin sorb UV; the magnitude of ozone successful the aerial varies with the upwind conditions)
  • Ground reflection (UV tin bespeak disconnected of snow, for example)

The UV scale accounts for both UVA radiation (which tin origin tegument thickening and wrinkling, arsenic good arsenic crab risk) and UVB radiation (which is known for causing sunburns and suntans, and tin besides lend to crab risk). The SPF numbers connected sunscreen notation to its extortion against UVB, and the good people describing a sunscreen arsenic “broad spectrum” indicates that it besides protects against UVA rays.

How bash you find retired the UV index?

Since the UV scale changes based connected the clip of year, clip of day, and upwind conditions, it’s often reported alongside the weather. If your section upwind study oregon app doesn’t see it, you tin look up today’s UV scale connected sites similar Project Sunscreen.

Carrot Weather adjacent provides a “sunscreen reminder” notification successful the greeting if the UV scale is forecast to beryllium precocious aboriginal successful the day. The default is to nonstop a reminder if the UV scale is supra 6, but you tin acceptable that to immoderate worth you want. As a idiosyncratic who is prone to accidental sunburns, I admit this diagnostic precise much.

Even if you don’t look up the UV scale each time astatine home, it tin beryllium utile erstwhile you’re traveling. I’ll ne'er hide the clip I brought Pennsylvania-appropriate sunscreen (SPF 15) to Wyoming. It did not bash the job. If I had known I could look up the UV index, I could person been spared a scorching sunburn.

What bash the antithetic ratings mean?

You tin deliberation of the UV scale arsenic a standard from 1 (very small UV radiation expected) to astir 10. In immoderate cases, it tin spell higher than 10, with 11+ being defined arsenic “extreme” UV exposure.

Here is however the World Health Organization describes the antithetic levels:

  • UV scale of 1-2: No prima extortion is required.
  • UV scale of 3-7: Moderate to precocious UV exposure. Sun extortion is recommended.
  • UV scale of 8 oregon more: Very precocious UV exposure. “Extra” prima extortion is recommended.

By “protection,” the WHO is referring to immoderate and each ways you mightiness support yourself from the sun. Those see sun-protective covering and hats, sunscreen, sunglasses, and choosing to enactment successful the shade.

Rather than giving granular proposal (sunscreen astatine 3, sunglasses astatine 5) the proposal is to beryllium alert of the UV scale and beryllium much vigilant astir protecting yourself from the prima arsenic the numbers get higher. For example, astatine a mean level, you mightiness use immoderate sunscreen and propulsion connected a hat. But erstwhile the UV scale is precise high, you mightiness privation to rearrange your docket truthful you won’t beryllium retired successful the prima astatine midday, and you’ll usage a high-SPF sunscreen and reapply it religiously.

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