SUNSTOKE

Sunburn Risk Category

The forecast is for open, flat ground. Add the water, sand or snow around you and your altitude, and see the WHO category for the UV you will actually get, with what WHO and the EPA say to do.

WHO: UV rises 10% to 12% with every 1000 meters; this tool adds 12%.

Your sunburn risk category

Category
High
UV with ground and altitude
UV 7 (6 to 7)
Forecast alone
UV 7, High
WHO says
“Seek shade during midday hours! Slip on a shirt, slop on sunscreen and slap on hat!”
EPA says
“Protection needed. Seek shade during late morning through mid-afternoon. When outside, generously apply broad-spectrum SPF-15 or higher sunscreen on exposed skin, and wear protective clothing, a wide-brimmed hat, and sunglasses.”
  • WHO: "Fair-skinned people suffer more from sunburn and have a higher risk of skin cancer than dark-skinned people; however, darker-skinned people also develop skin cancers."
  • WHO: "Sunscreens should not be used for extending time spent in the sun."
  • WHO: "REPORTING BURN TIMES IS NOT RECOMMENDED. Hence, relating UVI values to “time to burn” or “safe tanning time” sends out the wrong message to the public."

The top of each WHO figure is added and any fraction rounds up, so the category can only read higher than the forecast. Sources: WHO UV Index guide, WHO, EPA.

The forecast plus what is around you

WHO’s guide to the UV index lists two things that push UV above the forecast: reflection from the ground and altitude. This tool adds the top of WHO’s figure for each, so the category it reports is never lighter than the forecast’s own. A day forecast at UV 6 over fresh snow reads Extreme.

It does not say how long you can stay out. From UV 3 up, WHO and the EPA say protection is needed: shade, clothing, a hat, sunglasses and sunscreen on the skin clothes cannot cover.

Frequently Asked Questions

Where do the water, sand and snow figures come from?

From WHO's Global solar UV index guide: "fresh snow can reflect as much as 80% of UV radiation, dry beach sand about 15% and sea foam about 25%." The tool adds the top of each figure (80% for snow, 25% for water, 15% for sand). WHO lists no figure for grass, so grass adds nothing.

How does altitude change things?

WHO: "With every 1000 metres increase in altitude, UV radiation levels increase by 10% to 12%." The tool adds 12% per 1000 meters, the top of that range.

Why is there no risk score or time to burn any more?

Until October 6, 2026 this tool turned your skin type, minutes outside and SPF into a score and a time to burn. WHO's guide says: "REPORTING BURN TIMES IS NOT RECOMMENDED. Hence, relating UVI values to “time to burn” or “safe tanning time” sends out the wrong message to the public." It now reports the category and the official actions only.

Does my skin type change the category?

No. The category describes the UV, not the person. WHO says: "Fair-skinned people suffer more from sunburn and have a higher risk of skin cancer than dark-skinned people; however, darker-skinned people also develop skin cancers."

Does a high SPF make me safe for the whole day?

No. WHO: "Sunscreens should not be used for extending time spent in the sun." The FDA: "Reapply sunscreen at least every two hours, and more often if you're sweating or swimming."

General information, not medical advice. The words in quotation marks are WHO’s, the EPA’s and the FDA’s, checked on their sites on October 6, 2026.