UV index explained, when sunscreen really matters

The numbers

• 0 to 2 (Low). Sunscreen optional unless you're out for hours. Most winter days.
• 3 to 5 (Moderate). SPF 30 if you're outside for more than 30 minutes. A hat helps.
• 6 to 7 (High). SPF 30 minimum, hat, sunglasses, seek shade between 11 and 3.
• 8 to 10 (Very high). SPF 50, cover up, avoid 11 to 3 if you can. Skin burns in under 25 minutes.
• 11 and up (Extreme). Stay inside at peak hours. Skin can burn in 15 minutes.

What the SPF number really tells you

SPF 15 blocks 93% of UVB. SPF 30 blocks 97%. SPF 50 blocks 98%. SPF 100 blocks 99%.

The jump from 30 to 50 is small but worth it if you have fair skin or you're outside in strong UV. Don't pay extra for SPF 70+ thinking it's miles better. It isn't.

Reapplication matters more than the number

Most people apply too thin a layer and never reapply. The rule of thumb:

• A teaspoon for the face
• A tablespoon for each arm or leg
• A shot glass for the whole body

Reapply every two hours, and after swimming or sweating.

Mineral vs chemical sunscreen

Mineral (zinc, titanium): Works straight away, gentler on sensitive skin, doesn't sting eyes. Slight white cast.

Chemical (avobenzone, octocrylene): Lighter feel, invisible. Needs 20 minutes to absorb before sun exposure. Can irritate sensitive skin.

Cloudy days are sneaky

Up to 80% of UV passes through light cloud. Snow, sand, and water reflect UV back at you, adding 25 to 80% extra exposure. A cloudy day at the beach has burned more people than a sunny day in the city.

Today's UV

Open Window Today's UV card pulls live UV index data and tells you what protection level you actually need.

What the UV index numbers actually mean for your skin

The UV index is a scale of how strong the sun's ultraviolet radiation is at ground level. From 0 to 2 is low and you can be outside safely with little protection. From 3 to 5 is moderate and 6 to 7 is high; both call for sunscreen, a hat, and shade in the middle of the day. From 8 to 10 is very high and 11 or above is extreme, levels at which unprotected skin can start to burn in well under fifteen minutes. The crucial point most people miss is that the index is about UV strength, not temperature, which is why you can get badly burnt on a cool, breezy day that did not feel hot at all.

The shadow rule and timing your day

You do not need an app to gauge the risk. The shadow rule is a reliable shortcut: if your shadow is shorter than your height, the sun is high and UV is strong, so protection matters. UV peaks around the middle of the day, roughly 10am to 4pm in summer, when the sun is highest. Scheduling outdoor work, sport, and beach time for the early morning or late afternoon dramatically cuts your exposure. Clouds are not the protection they seem; up to 80% of UV passes straight through light cloud, which is why overcast summer days catch so many people out.

Using sunscreen properly, because most people do not

Sunscreen only works at the dose it was tested at, and almost everyone applies far too little. For an adult that means roughly a teaspoon for the face and neck and about a shot glass worth for the whole body, applied 20 minutes before going out and reapplied every two hours, and immediately after swimming or heavy sweating. A broad-spectrum SPF 30 or higher is the baseline. Sunscreen is the last line, though, not the first: shade, a wide-brimmed hat, sunglasses, and covering clothing block far more UV than lotion alone, and they do not wear off.

Frequently asked questions

What UV index level do I need sunscreen?

From 3 upward. At an index of 3 to 5 use sunscreen and a hat for extended time outside, and at 6 and above protection is essential, including seeking shade in the middle of the day.

Can I get sunburnt on a cloudy day?

Yes. Light cloud lets through up to 80% of UV, so the index can stay high under an overcast sky. Judge by the UV index, not by how sunny or warm it looks.

Does a higher SPF mean I can stay out longer?

Not reliably. SPF 30 blocks about 97% of UVB and SPF 50 about 98%, a small difference, and both wear off and need reapplying every two hours. High SPF is not a licence to skip reapplication or shade.

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