Cloud does not block UV the way it blocks sunshine. Here is what actually reaches your skin on a grey day, and when sunscreen genuinely matters.

Quick look

1. Over 90% of UV rays can pass through cloud, so sunburn is possible in the UK on grey and cool days.
2. Check the UV index on a weather app: at 3 or higher, protecting your skin with shade, clothing and SPF is advised.
3. Use sunscreen of at least factor 30 with 4-star UVA protection, apply it generously and reapply every 2 hours outdoors.
4. You cannot feel UV or judge it by temperature; the shadow rule and a forecast are better guides.
5. Babies under 6 months should be kept out of direct sunlight, as sunscreen is not recommended for them.

Grey skies, a chill in the air, and the sunscreen stays in the bathroom cabinet. That is the routine for plenty of people in the UK, and the reasoning sounds sensible: no visible sun, nothing to protect against. The trouble is that UV rays, the ones that actually damage skin, behave nothing like sunshine or warmth. Here is how to separate the myths from the facts on cloudy days.

Myth: Clouds Block the Rays That Burn

Cloud blocks light and some warmth, but it is surprisingly poor at blocking ultraviolet radiation. NHS guidance notes that over 90% of UV rays can pass through cloud, and Met Office advice says up to 80% of the sun’s UV rays penetrate light clouds. That is why sunburn happens in the UK on grey, cool and foggy days, not just on holiday.

The damage adds up quietly. Most skin cancers are caused by sun exposure over a long period, or by a history of sunburn, because UV damages the DNA in skin cells and the body does not always repair it fully. A day you never feel burning can still be a day your skin takes a hit.

Fact: The UV Index Does the Thinking for You

You cannot judge UV by looking out of the window, but you do not have to guess. Weather apps and the Met Office forecast show the UV index, a scale developed by the World Health Organization. If the index is 3 or higher, the NHS advice is to consider protecting your skin.

The index comes with its own guidance:

Index level	What the advice says
Low	Everyday time outdoors is fine; sunscreen is still worth thinking about in direct sun
Moderate	Be extra careful around the middle of the day, limit time in the sun without protection and put sunscreen on
High	Stay in the shade around midday, keep your skin covered and use sunscreen
Very high	Keep out of the sun between 11am and 3pm where you can, or find shade, with covered skin, sunscreen and a hat as the minimum
Extreme	Stay out of the midday sun altogether, with covered skin, sunscreen and a hat treated as essentials

The Met Office app and website show UV forecasts for the next 7 days, with an hour-by-hour breakdown for the next 2 days, so you can plan a walk or a day out around it.

Myth: You Can Feel When the Sun Is Strong

You cannot feel UV rays, which is exactly why temperature is such a poor guide. The sun can be strong enough in the UK to damage skin even when it is cold or cloudy. If you want a rough check without a forecast, use the shadow rule: when your shadow is shorter than your height, the sun’s UV rays are strong.

People underestimate this constantly. Survey findings reported by the Met Office found a quarter of people think UV is only harmful when the sky is clear, a quarter believe it does no harm after 3pm, and 27% think there is no need to worry when it is cold. Your eyes are at risk too: they are around 10 times more sensitive to UV than skin. Sunglasses with proper UV protection help whatever the weather, because a darker lens alone does not mean more protection.

Myth: Sunscreen Lets You Stay Out Longer

No sunscreen, whatever the factor, blocks 100% of UV, and NHS guidance is clear that you should not spend any longer in the sun than you would without it. Put it on to protect the skin that clothing and shade cannot cover, then reapply liberally every 2 hours, and straight after swimming, towel drying or sweating, even with a water-resistant formula. Water itself reflects UV, which can increase your exposure on a swim day.

Who Genuinely Needs SPF on a Cloudy Day

Cancer Research UK advice shared by the Met Office puts the UK’s burning season at roughly April to September, when the sun is capable of damaging skin even on a mild day. From spring to early autumn, a cloudy forecast is not a reason to skip protection if you will be outdoors for a while: check the index and act on it. Daily SPF earns its place when the UV index sits at 3 or above, or when you spend long stretches outside year-round.

A few balancing points. Vitamin D matters too, and people can often make enough by spending just a few minutes in the sun, so sensible protection does not mean avoiding daylight. There is no safe or healthy way to tan; a tan does not protect your skin from further UV damage, so if you like the look, fake tan is the safer route. And babies under 6 months should be kept out of direct sunlight entirely, as sunscreen is not recommended for them.

Wearing SPF Without the Fuss

If a full sunscreen routine puts you off, keep it simple:

• Pick at least factor 30 with a 4-star UVA rating or better. The letters “UVA” in a circle mean it meets the EU standard, and products covering both UVA and UVB are called broad spectrum.
• Use enough. Most people under-apply, and thin layers reduce the protection. As a guide, an adult covering the whole body needs around 6 to 8 teaspoons; for a normal day, think face, neck and ears at minimum.
• Reapply every 2 hours outdoors, and after water or towel drying.
• Check the expiry. The open jar symbol with an M and a number shows how many months the product lasts once opened, the same symbol we explain in our guide to how long makeup lasts.

Sunscreen slots into a morning just as easily as moisturiser. Layer it on before makeup and it sits comfortably under anything from a full face to a five-minute everyday routine. It is also worth picking something you will actually use rather than the priciest option on the shelf; our breakdown of the real cost of a year of sunscreen shows what a workable daily habit adds up to.

Little trick: Check the UV index alongside the weather each morning. If it reads 3 or above, sunscreen goes on before you leave the house, even if the sky is grey.

Ask away

Can you get sunburnt through clouds in the UK?

Yes. Over 90% of UV rays can pass through cloud, and sunburn happens on cloudy British days, not just on holiday abroad.

What SPF should I use day to day?

The NHS advises sunscreen of at least factor 30 with a 4-star UVA rating or better. Apply enough to do the job and reapply every 2 hours if you are outdoors.

Do I need sunscreen in winter?

Check the UV index. If it is below 3, protection is less urgent, though people who spend long stretches outdoors year-round may still want SPF on exposed skin.

Does a darker lens in sunglasses mean more UV protection?

No. The shade of the lens is not what protects you. Look for sunglasses with proper UV protection, whatever the tint.