UV Index Today

Real-time solar radiation monitoring

UV Index Guide

FAQ-style answers on sunscreen and solar UV, compiled by UV Index Today editors from WHO, FDA, EPA, and IARC public guidance—and from running the live index. Each page lists sources. For field notes and dated weather, see the Blog.

Sunscreen Essentials

Does Sunscreen Expire?

Yes—usually within three years, and heat-damaged bottles may underperform.

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Does Sunscreen Prevent Tanning?

It slows tanning but won't stop it if UVA gets through or you under-apply.

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How Long Does Sunscreen Last?

Reapply every two hours—sooner if you're swimming, sweating, or toweling off.

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Does Sunscreen Cause Cancer?

No—UV causes skin cancer; sunscreen lowers that risk.

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How Does Sunscreen Work?

It reflects UV or absorbs it and turns it into heat—either way, less reaches your cells.

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What Does SPF Stand For in Sunscreen?

Sun Protection Factor—how well a product blocks UVB, not how long you can stay outside.

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Everyday UV Protection

What UV Index Requires Sunscreen?

The WHO treats UV index 3 as the line to start protecting skin.

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Does Glass Block UV Light?

Regular glass blocks most UVB but lets a lot of UVA through.

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Do Car Windows Block UV?

Windshields block most UVA; side windows do not.

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UV & Your Health

What Are Good UV Rays for Tanning?

There aren't any—tanning is your skin's response to UV damage.

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Can UV Light Cause Cancer?

Yes—solar UV and tanning-bed UV are classified as known human carcinogens.

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UV Index Records

What Is the Highest UV Index Ever Recorded?

The figure usually quoted is about 43.3, measured at Bolivia's Licancabur volcano in 2003.

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What Place Has the Highest UV Index?

Routine extremes sit in the high Andes, where altitude and latitude stack.

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