UV Index Statistics & Facts

The UV Index Scale

• The UV index is an open-ended international scale developed by the World Health Organization and partner agencies; values of 3+ call for sun protection, and 11+ is classified "extreme."
• UV radiation is typically strongest between 10 AM and 4 PM, and around solar noon the sun delivers UV at its daily maximum even when temperatures feel mild (EPA).
• Up to 80% of UV radiation can penetrate light cloud cover — overcast days are not safe days (WHO).

Skin Cancer in the United States

• Skin cancer is the most common cancer in the United States (CDC).
• About 1 in 5 Americans will develop skin cancer by the age of 70 (Skin Cancer Foundation).
• Roughly 5.4 million basal and squamous cell skin cancers are diagnosed in about 3.3 million Americans each year (American Cancer Society).
• More than 100,000 new cases of invasive melanoma are expected in the US in 2026 (American Cancer Society).
• About 90% of nonmelanoma skin cancers are associated with exposure to UV radiation (Skin Cancer Foundation).
• Having five or more sunburns in a lifetime roughly doubles the risk of melanoma (Skin Cancer Foundation).
• Treating skin cancer costs the US healthcare system an estimated $8.9 billion per year (CDC).

What Changes Your UV Exposure

• Altitude: UV levels increase by roughly 10% with every 1,000 meters (about 3,300 feet) of elevation — the reason high-altitude Flagstaff and Santa Fe rank #2 and #3 among America's fastest-burning cities, ahead of nearly all of Florida (WHO).
• Snow: fresh snow can reflect up to 80% of UV radiation, nearly doubling effective exposure — the physics behind winter goggle tans (WHO).
• Sand and water: dry beach sand reflects about 15% of UV and sea foam about 25%, which is why beach exposure exceeds the forecast index (WHO).
• Depth: UV penetrates water — swimmers can burn below the surface, and wet skin burns faster than dry skin (EPA SunSafety).
• Shade: effective shade can cut UV exposure by 50% or more, making it one of the simplest protective measures (EPA SunSafety).

Sunscreen and Protection

• Regular daily use of SPF 15+ sunscreen has been shown to reduce melanoma risk by about 50% and squamous cell carcinoma risk by about 40% (Skin Cancer Foundation).
• Most Americans don't use sunscreen regularly: fewer than a third of women and about 15% of men report routinely using it on both their face and other exposed skin (CDC).
• Using an indoor tanning bed before age 35 increases melanoma risk by as much as 75% (American Academy of Dermatology).
• UV damage is cumulative across all skin types — darker skin burns more slowly but is not immune, and skin cancer in people of color is often diagnosed later (AAD).

City-Level UV Data

For live UV readings, hourly forecasts, and safe exposure times in your city, use the UV Index Checker tool or browse UV index by city. For our own analysis of which US cities burn fastest — computed clear-sky UV for the 500 largest cities, with the full dataset downloadable — see the 2026 UV Rankings.