The Canaries burn people who would never burn at home, because the sun here is far stronger than the temperature suggests and the trade wind keeps your skin feeling cool while it happens. Sunburn is comfortably the most common thing that ruins a Canarian holiday, and almost all of it happens on day one or day two, before anybody has worked out how different this light is.

The islands sit at roughly 28 degrees north, which puts them level with the Florida Keys and the northern edge of the Sahara rather than with anywhere in Europe. The sun climbs much higher in the sky than it does over Britain or Ireland, so its rays pass through less atmosphere and arrive with more ultraviolet in them. That is true in January as well as July.

None of this needs to be frightening. It needs a factor 30 or 50 cream applied properly, a hat, a sensible attitude to the middle of the day, and an understanding that a breeze is not shade. Get those right and you will come home brown rather than peeling.

Why the UV index stays high all year

The UV index is a measure of how quickly unprotected skin will be damaged. In the UK it rarely passes 7, and for half the year it barely registers. In the Canaries it routinely reaches 10 or 11 in summer — the band officially described as extreme — and even in December and January it commonly sits around 4 or 5, which is the level a British summer afternoon reaches.

Two things push it higher still. Altitude adds roughly ten per cent more UV for every thousand metres you climb, which is why a morning at the Teide cable car is one of the easiest places in Europe to burn badly in cold air. And reflection adds more: pale sand, water and the white walls of a resort all bounce light upward, so you catch it on your chin, your nose and the underside of your arms where you never think to put cream.

UV is not the same thing as heat. It is not blocked by cloud in any reliable way — a bright overcast day on the north coast of Tenerife can deliver most of the UV of a clear one. People burn under the panza de burro, the grey cloud blanket described on our page about how the island climate actually works, precisely because it does not feel like burning weather.

The trade wind that hides the damage

This is the specific Canarian trap. The alisios blow from the north-east for most of the year, and they are cool because they have crossed the cold water of the Canary Current. On a beach at Corralejo or El Médano the wind keeps your skin at a comfortable temperature, evaporates the sweat that would otherwise warn you, and dries your sun cream off faster than you expect.

The feedback loop that tells you to move into the shade at home — getting uncomfortably hot — simply does not trigger. You realise what has happened at seven in the evening in the shower. People who have holidayed happily in the Mediterranean for thirty years get caught by this on their first Canarian trip, and if you want the fuller picture of the wind itself, our page on the island breeze explains where it blows hardest.

The hours that matter

The strongest UV falls roughly between midday and four in the afternoon. That is later than the British "eleven to three" rule, and there is a neat reason why: the archipelago keeps the same clock as London and Dublin, but it lies around sixteen degrees further west. Solar noon — the moment the sun is genuinely at its highest — falls at about half past one in winter and closer to half past two during summer time. The clock is lying to you by an hour and a half.

Which is convenient, because it lines up perfectly with the local habit of eating lunch at two. Follow what Canarians do, described in more detail in our guide to island opening hours and the long midday break, and you will be indoors or under an awning for the worst of it without feeling you have missed anything. Go back out at four, when the light softens and the Maspalomas dunes turn gold, and you get the best part of the day anyway.

Factor, stars and how much to use

NHS guidance is to use a sunscreen with at least SPF 30 and a UVA rating of four or five stars. For this latitude, treat 30 as the floor and 50 as the sensible default for the first few days, for children, and for anyone fair. The SPF number describes protection against UVB, the burning radiation; the stars or the circled UVA mark describe protection against the deeper, ageing radiation. You want both.

The bigger problem is quantity. Laboratory SPF figures assume two milligrams of cream per square centimetre of skin, which works out at roughly six to eight teaspoons for an adult body — around a shot glass. Almost nobody applies that much, and applying half the quantity does not give you half the protection, it gives you considerably less. A family of four on a week's beach holiday should expect to get through more than one bottle.

Clothing beats cream

A long-sleeved cotton shirt does not need reapplying and does not wash off. The Canarian answer to strong sun, long before sunscreen existed, was a wide-brimmed hat and covered arms, and it is still the right answer for a day walking. On the water — a whale-watching trip off Los Gigantes, a kayak, a ferry deck — a rash vest is worth more than any cream, because the reflection off the Atlantic doubles your exposure and the spray removes whatever you applied.

Sunglasses matter too, and not only for comfort. The same UV that burns skin damages the surface of the eye, and glare off pale sand is intense. Anything sold in the EU carries a CE mark and gives full UV protection; cheap market stalls sell tinted plastic that does not, and dark lenses without UV filtering are worse than none because your pupils open wider behind them.

Reef-safe cream, and whether it matters here

Chemical filters, particularly oxybenzone and octinoxate, have been linked in research to coral bleaching and to harm in other marine organisms. Several jurisdictions, including Hawaii and Palau, have banned them outright. Spain has not, so nothing stops you buying ordinary cream here.

The Canaries have very little true coral, but they do have volcanic reefs, seagrass meadows and a lot of marine life in a small area — the rockpools and shallow lagoons described on our page about the islands' natural swimming pools are enclosed bodies of water where thousands of people swim each week and the flushing is slow. Mineral creams using zinc oxide or titanium dioxide are an easy swap. They are thicker, sometimes leave a faint white cast, and are widely sold in island pharmacies. If you swim in the charcos, use one.

If you have already burned

Get out of the sun entirely, and stay out of it for the rest of the day — not under a parasol, indoors. Then:

See a pharmacist if there is extensive blistering, if you feel sick, shivery or dizzy, or if a child or baby is affected. Spanish pharmacists deal with this daily and stock stronger preparations than a British chemist will sell you, and our guide to using a farmacia and the out-of-hours rota explains how to find one at any hour. Heatstroke — confusion, a very high temperature, no sweating — is a 112 call, not a pharmacy visit.

Children, babies and the water

Babies under six months should be kept out of direct sun altogether, and small children need a hat with a neck flap, a rash vest and cream on everything else. The sea helps not at all: water transmits UV to a depth of half a metre or more, and a child snorkelling face-down for an hour will cook the backs of their legs. The practical version of all this sits in our guide to holidaying here with children.

The bottom line

Treat the first two days as the dangerous ones, use more cream than feels reasonable, cover up between midday and four, and remember that the cool wind is not your friend. Everything else about the Canarian climate is forgiving — the sea stays swimmable most of the year — and the wider advice on staying safe on the islands covers the rest. The sun is the one thing here that genuinely deserves respect, and respecting it costs about ten euros and five minutes a day.