Not by WHO’s categories: 10 is the top of the Very high band (8 to 10), and Extreme begins at 11. It is one point below the highest named category.

WHO category: Very high (8 to 10)

How long to get burned in UV 10?

At UV index 10, the erythemal-dose model computes a first-perceptible-reddening reference dose after roughly 13 minutes of continuous unprotected exposure for Fitzpatrick skin type I, and roughly 67 minutes for type VI. The full type I–VI table is below, with the arithmetic and the sources.

Computed from a dose rate of 9 standard erythema doses per hour at UV index 10. Reference values, not measurements of any individual.
Fitzpatrick skin type	Reference dose to first erythema (SED)	Minutes to that dose at UV 10	0.6 × that figure (min)
Type Ialways burns, never tans	2	13	8
Type IIusually burns, tans minimally	2.5	17	10
Type IIIsometimes mild burn, tans uniformly	3.5	23	14
Type IVburns minimally, always tans well	4.5	30	18
Type Vvery rarely burns, tans easily	6	40	24
Type VIdeeply pigmented, never burns	10	67	40

The fourth column is a fixed 0.6 multiple of the third — an arithmetic margin for the roughly ±30–50% spread in published reference doses within one phototype. It is what the app reports.

“Reporting burn times is not recommended.”

— WHO, WMO, UNEP and ICNIRP, Global Solar UV Index: A Practical Guide, WHO/SDE/OEH/02.2 (2002)

The guide gives its reasoning directly: “people tend to interpret burn times to mean that there is a safe level of unprotected sun exposure”, and relating index values to a time to burn therefore “sends out the wrong message”.

Why we publish the figure anyway →

This page answers the UV 10 question. The app answers yours.

Real days do not sit at 10 — the index climbs to a peak and falls again. Safe Sun Window takes your skin type and the index where you actually are, and runs this same calculation on those inputs. Free, no account, no ads. Return visits are counted with a random first-party id that goes to no one else. If you turn on location, your device rounds your position to about 10 km before it reaches our weather provider for the UV reading, with no id attached.

Open Safe Sun Window →

What UV 10 means

Ten is the top of WHO’s Very high band and the last reading before Extreme. It is also the point where the received dose and the reported index can diverge most: the index is defined for a horizontal surface, but a person on snow, sand or water receives that downwelling radiation plus whatever the ground sends back up.

WHO quantifies the reflection: fresh snow can reflect as much as 80% of UV radiation, sea foam about 25%, and dry beach sand about 15%. None of that changes the number on the forecast; all of it changes the dose. At half a metre depth, WHO notes, UV is still 40% as intense as at the surface.

Where and when UV 10 actually occurs

Ten is what a high sun produces when nothing much is damping it: no cloud, little aerosol, and often some altitude. Readings of 10 typically come from:

Tropical and subtropical midday under clear skies for much of the year.
The summer peak in the sunnier, drier southern mid-latitudes.
High-altitude tropical and subtropical sites, where the altitude effect compounds an already-high base reading.
Clear-sky conditions with low aerosol loading — WHO notes that predicting the index requires both total ozone and aerosol optical properties as inputs.

A peak of 10 implies a broad elevated middle to the day rather than a spike: WHO’s figure that about 60% of daily UV arrives between 10 a.m. and 2 p.m. describes the same concentration at every level, but at 10 the absolute dose inside that window is large.

The six factors WHO lists as setting the index, with its own figures →

What the published guidance says at UV 10

The US EPA publishes for 8 and above: “Extra protection needed. Be careful outside, especially during late morning through mid-afternoon. If your shadow is shorter than you, seek shade and wear protective clothing, a wide-brimmed hat, and sunglasses, and generously apply a minimum of SPF-15, broad-spectrum sunscreen on exposed skin.”

The WHO guide’s own reinforcement point is well below 10: it states that protection is necessary above a threshold value of 3 “and this message should be reinforced at UVI values of 8 and above”, which puts every reading in the Very high band, 10 included, inside that reinforced range.

The published scheme is binary, not graded: the same measures apply from UV 3 upward, and what changes with the index is the rate at which erythemal dose accumulates. Why the scheme is not graded →

Check the arithmetic

At UV 10, an hour of continuous exposure delivers 10 × 0.9 = 9 standard erythema doses. Fitzpatrick type II’s reference dose is 2.5 SED, so 2.5 ÷ 9 × 60 = 17 minutes. Every row in the table above is that division with a different reference dose.

The 0.9 factor is exact, and follows from the definition of the index; the reference doses are not. Where the 0.9 comes from, and what the reference doses are →

Questions

How long to get burned in UV 10?: At UV index 10 the model computes a first-erythema reference dose in about 13 minutes of continuous unprotected exposure for Fitzpatrick type I skin and about 67 minutes for type VI. These are computed model outputs for a reference dose, not durations of demonstrated safety.
Is UV 10 extreme?: Not by WHO’s categories: 10 is the top of the Very high band (8 to 10), and Extreme begins at 11. It is one point below the highest named category.

Other UV levels

All levels, the full method, and why burn times are contested →

Sources for the figures above

World Health Organization, World Meteorological Organization, United Nations Environment Programme and International Commission on Non-Ionizing Radiation Protection. “Global Solar UV Index: A Practical Guide.” WHO/SDE/OEH/02.2, 2002.
ISO 17166:1999 / CIE S 007/E-1998. Erythema reference action spectrum and standard erythema dose.
United States Environmental Protection Agency. “UV Index Scale.” epa.gov, last updated 15 June 2026; verified 3 August 2026.
Fitzpatrick TB. “The validity and practicality of sun-reactive skin types I through VI.” Archives of Dermatology, 1988;124(6):869–871.
Minimal-erythema-dose values per Fitzpatrick phototype — working reference values, range-checked against ISO 17166:1999; the six-value progression itself is not traced to a named primary document.

Full annotated source list, with what each one is used for →