The WHO scale ends at "11+ — extreme", but the physical maximum at Earth's surface is much higher. Let's look at the real records.
Where UV Hits 12–14 at Sea Level
- Atacama Desert, Chile — regularly 12–14 in summer;
- Altiplano (Bolivia, Peru) — 12+ in December–January;
- Arabian Peninsula — 11–12 in June–July;
- equatorial Africa and Indonesia — year-round 11–12.
The Absolute Record: Above 20
In 2003, researchers measured UV index 23.7 on the Licancabur volcano (5916 m) on the Chile–Bolivia border. The combination of high altitude (+50% per 3000 m), low ozone and thin atmosphere created a UV level unmatched anywhere else on Earth.
Why Equator Alone Isn't the Factor
| Factor | Effect |
|---|---|
| Latitude | closer to equator = higher, but not decisive |
| Altitude | +10–12% per 1000 m — huge effect |
| Ozone layer | thinner = more UV |
| Surface reflection | snow and salt flats multiply exposure |
That's why the Atacama, not equatorial Amazon, holds the records: altitude + dry atmosphere + reflective salt flats.
What This Means for Normal Life
At UV 15, unprotected skin burns in under 5 minutes. No sunscreen alone is sufficient — you need full UPF clothing, UV400 goggles and avoidance of open sun. Tourists visiting the Andes or high-altitude ski resorts routinely underestimate the risk.
Bottom Line
The theoretical maximum is around 25; the real record is 23.7. For comparison, check your city's UV: even "hot" European cities rarely exceed 9–10. But if you travel to the Andes, Himalayas or East African highlands — prepare for extreme protection.