The WHO scale ends at the "11+ — extreme" category. A value of 12 is the upper boundary of what's ever measured at Earth's surface.
Where UV Index 12 Occurs
- equatorial countries: Indonesia, Kenya, Ecuador — year-round;
- deserts and highlands: Tibet, Andes, Australia in summer — up to 12–14;
- Middle East and Central Asia in June–July: Dubai, Riyadh — 11–12;
- mountain resorts: +10–12% index per 1000 m of altitude.
Does 11–12 Occur in Europe or North America?
Extremely rarely. The maximum for southern Europe and US south is 9–11 on clear July days (Sicily, Athens, Phoenix, Miami). In temperate zones the ceiling is 7–8. Values of 12 are physically almost impossible at these latitudes.
What to Do at Index 11–12
- avoid open sun from 10:00 to 16:00;
- SPF 50+ every 2 hours, dense UPF clothing, wide-brim hat;
- only UV400 sunglasses — snow and sand reflect up to 80% of UV;
- don't take children outdoors at midday at all.
At this index a burn develops faster than you notice discomfort. Check the hourly chart on your city page — for example Dubai or Bangkok.