UV Index Sunscreen Guide: Five Colors, Three Sets of Instructions

Affiliate links below, but they cost you nothing extra. We only point you to what the ingredient lists actually back up.

Your weather app has a UV number in it right now, and probably a color behind it. The color has five settings. The instructions behind the color have three.

Where the five colors come from

One document, and it’s older than most people assume.

The five names come from Global Solar UV Index: A Practical Guide, published in 2002 as a joint recommendation of the WHO, the World Meteorological Organization, the UN Environment Programme and ICNIRP.^[1] Its Table 1 is what your app is coloring in:

Exposure category	UVI range, as printed
Low	<2
Moderate	3 to 5
High	6 to 7
Very high	8 to 10
Extreme	11+

Look at the top row of that table and then at the color chart later in the same document, which writes the Low band as (1,2) and gives it green.^[1] The WHO’s current public Q&A writes the same band as 0 to 2.^[2] Three printings, three edges. Nothing rides on it for a reader, but it’s a fair warning about how much precision to read into a single digit.

The app says 8 today. What do I do differently than at 6?

By these agencies’ own tables, nothing different in kind. You stay out of the midday sun harder.

The EPA groups 3 through 7 together and tells you: “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.”^[3]

For 8 and up it says: “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.”^[3]

Read those two side by side. The wording shifts, but the sunscreen instruction is the same in both, down to the same minimum SPF. The WHO’s version escalates in the same place: at 3 to 7 it says “Seek shade during midday hours!”, and at 8 and above it says “Avoid being outside during midday hours!”^[2]

So a rising index is an argument about your calendar, not about your shopping. If you want the lever that actually moves your protection, it’s how much you put on, and we measured that out in our how-much guide.

The number is a forecast, and it’s a maximum

It describes a four-hour window, not your afternoon.

The 2002 guide sets out how the figure is supposed to be reported, and the details change how you should read it:^[1]

• Reports present the daily maximum, which happens in the four-hour period around solar noon. Depending on where you are and whether daylight saving applies, solar noon lands between local noon and 2 p.m.
• It’s given as a single value rounded to the nearest whole number, so a 5 and a 6 can be much closer than they look.
• When cloud cover is variable it’s supposed to be given as a range, and forecasts that don’t model cloud at all should be labeled “clear sky” or “cloud free”.

That last one is the one to keep. A forecast made without cloud in it is a description of the sky you might have had. Cloud is also a worse filter than it looks, which is the whole subject of our cloudy day piece.

Underneath, the index is weighted to erythema, the skin reddening reaction that shows up as sunburn, using a standard reference curve.^[1] It is a sunburn-shaped measurement. It is not a measurement of the aging wavelengths that reach you through a window, which is why the desk-by-the-window question doesn’t get answered by this number at all.

Can I skip sunscreen when the index is 1 or 2?

Here is exactly what each agency prints, and then where the printing stops.

The EPA, for 1-2 Low: “No protection needed. You can safely stay outside using minimal sun protection.”^[3] The WHO, for 0 to 2: “You can safely enjoy being outside!”, with this line under the table: “Even for very sensitive fair-skinned people, the risk of short-term and long-term UV damage below a UVI of 2 is limited, and under normal circumstances no protective measures are needed.”^[2]

That’s the whole of it, and it’s worth noticing what it isn’t. It’s a band on a forecast daily maximum, not a verdict on your day, and neither agency turns it into a number of minutes. The 2002 guide is blunt about that second part. It states that reporting burn times is not recommended, because “people tend to interpret burn times to mean that there is a safe level of unprotected sun exposure”, and it adds that the index “should not imply that extending exposures is acceptable”.^[1] The same document says sunscreens “should not be used to increase sun exposure time but to increase protection during unavoidable exposure”.^[1]

One more thing the agencies do say plainly: 3 is the number that turns advice on. The WHO notes that some countries issue sun protection times when levels are forecast to be 3 or higher.^[2] A great many days in a great many places clear 3.

The check that works with no app at all

Look down. The EPA calls it the Shadow Rule.

In its words: “If your shadow is taller than you are (in the early morning and late afternoon), your UV exposure is likely to be lower. If your shadow is shorter than you are (around midday), you are being exposed to higher levels of UV radiation.”^[3]

It’s free, it works with a dead phone, and it reports the moment you’re standing in rather than a forecast maximum. The EPA also states that the scale it uses “conforms with international guidelines for UVI reporting established by the World Health Organization”, so you aren’t switching systems when you cross a border.^[3]

What should I actually carry on a high index day?

Four of the five things on those lists aren’t products: shade, a shirt, a hat, sunglasses. The fifth is the one you can get wrong by not reapplying it.

Since a high reading is really an instruction about midday hours, the useful purchase is whatever makes a midday top-up survive contact with reality. A tube you have to rub in with sunscreen already on your face usually loses. Two picks, chosen on their labels and their format rather than on any sun-strength claim:

Start here for the top-up. Beauty of Joseon Matte Sun Stick. Four UV filters, at positions 11, 12, 15 and 17 of a 48-line list: Uvinul A Plus, Tinosorb S, Uvinul T 150 and Polysilicone-15.^[4] Neither zinc oxide nor titanium dioxide appears anywhere on it, so nothing in this stick can go chalky the way a mineral filter does.^[4] Silica is ninth and boron nitride thirteenth, which is where the matte finish comes from.^[4] The page shows two flags: alcohol-free, plus fragrance and essential oil free.^[4] A thing to note: nobody, this brand included, is claiming a stick survives sweat for a set number of minutes, and a stick is the format where getting a full dose on is hardest to verify. Check the price on YesStyle. Technique for going over makeup is in our stick guide, and the timing in our reapply piece.

For the morning layer under it, Isntree Hyaluronic Acid Watery Sun Gel. Six filters, unusually high up: positions 3, 4, 7, 9, 10 and 11 of a 43-line list, being ethylhexyl salicylate, homosalate, Tinosorb S, Tinosorb M, Polysilicone-15 and Uvinul A Plus.^[5] Both flags are on this page too.^[5] One trade-off: Tinosorb M is the chemical filter that behaves most like a mineral one, so it can show on deeper tones, and our white cast piece covers who that catches. Our longer look at this one is here. Check the price on YesStyle.

The short version of this UV index sunscreen guide

Read the number for time, not for SPF.

Below 3, both agencies print reassurance and stop there. From 3 up, the same instruction appears and doesn’t change ingredient by ingredient as the number climbs. From 8 up, the instruction gets more insistent about the same four midday hours the forecast was measuring in the first place. And if you’d rather not open anything at all, your shadow already told you.

FAQ

What UV index do I need to start wearing sunscreen?

Both agencies put the switch at 3. The EPA labels 1-2 as “No protection needed” and 3-7 as “Protection needed,” and the WHO notes that some countries issue sun protection times when levels are forecast to be 3 or higher.

Do I need a higher SPF when the index is 9 or 10?

Neither agency asks you to. The EPA prints the same minimum, broad-spectrum SPF-15 or higher, in both the 3-7 row and the 8+ row. What changes between the rows is the advice about being out at midday.

Why does my app say 6 in the morning when it doesn’t feel like it?

Because the reported figure is the day’s maximum, which occurs in the four-hour period around solar noon, and solar noon falls between local noon and 2 p.m. depending on your location. It is a forecast peak, not a live reading of 9 a.m.

How long can I stay out at a given UV index?

There’s no published answer to give you. The WHO guide states that reporting burn times is not recommended, because people read them as meaning there’s a safe level of unprotected exposure, and it says the index should not imply that extending exposures is acceptable.

Can I trust the index on a cloudy day?

Only if the forecast modeled cloud. The WHO guide says forecasts that leave cloud out should be labeled “clear sky” or “cloud free,” and that when cloud cover is variable the index should be given as a range rather than one number.

Sources

Agency documents (read directly):
[1] Global Solar UV Index: A Practical Guide, WHO/SDE/OEH/02.2, 2002, a joint recommendation of the World Health Organization, World Meteorological Organization, United Nations Environment Programme and the International Commission on Non-Ionizing Radiation Protection. Table 1 “UV radiation exposure categories” prints Low <2, Moderate 3 to 5, High 6 to 7, Very high 8 to 10, Extreme 11+; Table 4 “Presenting the UVI: International colour codes” writes the same bands as Low (1,2), Moderate (3,4,5), High (6,7), Very high (8,9,10), Extreme (11+); reporting section states that reports present the daily maximum occurring in the four-hour period around solar noon, that solar noon falls between local noon and 2 p.m., that the UVI “should be presented as a single value rounded to the nearest whole number,” that where cloud cover is variable it “should be presented as a range of values,” and that programmes not incorporating cloud effects “should refer to them as a ‘clear sky’ or ‘cloud free’ UVI”; states “REPORTING BURN TIMES IS NOT RECOMMENDED,” that “people tend to interpret burn times to mean that there is a safe level of unprotected sun exposure” and that the UVI “should not imply that extending exposures is acceptable”; Table 3 states sunscreens “should not be used to increase sun exposure time but to increase protection during unavoidable exposure”; Annex C defines the UVI from the CIE reference action spectrum for UV-induced erythema (ISO 17166:1999/CIE S 007/E-1998). Copy read: the PDF hosted by ICNIRP: link
[2] World Health Organization, “Radiation: The ultraviolet (UV) index,” Questions and answers, dated 20 June 2022. Action table has three rows: 0 to 2 “You can safely enjoy being outside!”; 3 to 7 “Seek shade during midday hours! Slip on a shirt, slop on sunscreen and slap on hat!”; 8 and above “Avoid being outside during midday hours! Make sure you seek shade! Shirt, sunscreen and hat are a must!” Also states “Even for very sensitive fair-skinned people, the risk of short-term and long-term UV damage below a UVI of 2 is limited, and under normal circumstances no protective measures are needed,” that reporting provides “the maximum daily UV level, which occurs during the four-hour period around solar noon,” and that “in some countries, sun protection times may also be issued when UV levels are forecast to be 3 or higher”: link
[3] US Environmental Protection Agency, “UV Index Scale,” page last updated June 15, 2026. Three bands: “1-2: Low. No protection needed. You can safely stay outside using minimal sun protection.”; “3-7: Moderate to High. 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.”; “8+: Very High to Extreme. 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.” Also carries the Shadow Rule as quoted, and states that “the UV Index scale used in the United States conforms with international guidelines for UVI reporting established by the World Health Organization”: link

Ingredient lists (INCIDecoder, read directly):
[4] Beauty of Joseon Matte Sun Stick: 48 listed ingredients; four UV filters, at 11 (Diethylamino Hydroxybenzoyl Hexyl Benzoate), 12 (Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine), 15 (Ethylhexyl Triazone) and 17 (Polysilicone-15); Butyloctyl Salicylate at 14 is a solvent, not one of the filters; zinc oxide and titanium dioxide both absent from the list; Silica ninth and Boron Nitride thirteenth; the Highlights block carries two flags, read by eye, “#alcohol-free” and “#fragrance & essentialoil-free.” Version note: INCIDecoder carries four entries under near-identical names for this stick (Matte Sun Stick, Matte Sunscreen Stick, Matte Sun Stick : Mugwort+Camelia, and Matte Sun Stick: Mugwort + Camelia SPF50 PA++++). All four were opened. Their lists run to 48, 49, 47 and 46 lines and differ only in a few extract and emulsifier lines; all four carry the same four UV filters in the same order. The entry cited here is the one whose name matches the retail listing linked above: link
[5] Isntree Hyaluronic Acid Watery Sun Gel: 43 listed ingredients; six UV filters, at 3 (Ethylhexyl Salicylate), 4 (Homosalate), 7 (Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine), 9 (Methylene Bis-Benzotriazolyl Tetramethylbutylphenol), 10 (Polysilicone-15) and 11 (Diethylamino Hydroxybenzoyl Hexyl Benzoate); two flags on the Highlights block, read by eye, “#alcohol-free” and “#fragrance & essentialoil-free.” Version note: INCIDecoder carries three entries for this gel (plain, “Spf50+ Pa++++”, and “SPF50 2025”). All three were opened; their lists run to 43, 40 and 43 lines, and all three place the same six filters at the same six positions: link