Almost everything a British person knows about the sun is wrong in the tropics, and the reason is geometry. At UK latitudes the sun is never directly overhead. Its path across the sky is a long shallow arc, so ultraviolet builds gently, peaks modestly and falls away over a long afternoon. In the tropics the sun climbs steeply to something close to overhead, sits there, and drops fast. The peak is far higher, the dangerous window is wider, and dusk is short.
The consequence is that the intuitions people bring with them, the sense that morning is fine, that four o'clock is safe, that a parasol is shade, that you can tell by how hot it feels, all fail at once.
The conditions, set out plainly
Equatorial or tropical destination, dry season
Conditions block- UV load
- Very high to extreme around the middle of the day, in the top bands of the World Health Organization index. The window of dangerous intensity opens earlier and closes later than in the UK.
- Water exposure
- Pool and sea, frequent, plus showers and towelling several times a day.
- Sweat
- Very high and continuous in heat and humidity, even at rest.
- Friction
- Moderate. Towels, clothing, sand, seating.
- Typical duration
- All day, every day, for one to three weeks.
- What fails first
- Everything, repeatedly, because the removal events are constant and nobody reapplies at the frequency the conditions demand.
- Protection strategy
- Shade and timing first, textile second, film third. Treat the middle of the day as indoor time, cover up outside it, and reapply after every swim, shower and towel dry.
Overhead sun destroys shade
Shade is a geometric relationship between you, the sun and an object. When the sun is low, an object throws a long shadow and shade is generous. When the sun is nearly overhead, the same object throws a small shadow directly beneath it. A parasol, a palm, a beach hut and a hat all lose most of their value at solar noon in the tropics, exactly when they are most needed.
Add reflection. Dry pale sand reflects ultraviolet, and so does water. That means that even in the shadow of a parasol, a person on a bright beach receives ultraviolet reflected from the surroundings. The World Health Organization's ultraviolet material describes surface reflectance, and our note on reflected ultraviolet covers what it means in practice. Shade reduces the dose. It does not remove it.
The reapplication clock
Reapplication clock: A day at a tropical latitude
The tropical day is not a British day scaled up. The peak is higher, arrives earlier and lasts longer. Mechanism only.
Sunscreen bought where you land
This is where the international angle stops being academic. A pack bought in a resort shop may have been made for the United States market, where sunscreen is regulated as an over the counter drug and the label follows a different set of rules. It may have been made for Australia, which has its own standard and its own regulator. It may be from the UK or EU regime, or it may be from a market with weaker enforcement altogether.
The practical differences matter. UVA indication is handled differently between regimes. Water resistance is expressed in minutes on a United States pack and as a category in the UK and EU. Words that are not permitted here appear routinely elsewhere. Our standards notes on the US position, the Australian standard and buying sunscreen abroad set out what changes and what does not.
The strategy
Timing is the strongest control
Moving beach time to early morning and late afternoon does more than any product. It reduces the dose rather than trying to block it, and it is the one control that cannot fail through misapplication.
Textile is the second strongest
A long sleeved linen shirt, a rash vest for the water, a wide brimmed hat. Locals in hot countries have generally worked this out already, and it is worth noticing what they wear rather than what visitors wear.
The film is third, and it has to be reapplied constantly
Every swim, every shower, every towel dry, every couple of hours regardless. The tropical day contains more removal events than a British one, and the dose between them is higher. Our note on reapplication covers the arithmetic of missing them.
Children and heads
Scalps, ears and the tops of feet burn on holiday more than anywhere else, on adults and children alike. Hats with brims, and a deliberate pass over the ears and feet. See scalp, ears and lips.
Do not rely on a tan
A tan is the skin's response to ultraviolet damage that has already happened. It is not a protective strategy and the NHS is clear that there is no such thing as a safe tan.
What the label will and will not tell you
Sunblock
What it certifies
Nothing. "Sunblock" is not a permitted claim on a sunscreen in the UK or the EU, because it conveys total protection, which cannot be substantiated. The European Commission recommendation underpinning sunscreen labelling advises against claims of this kind, and the retained UK framework for cosmetic claims requires that claims be supported by adequate evidence.
What it does not
It does not indicate a mineral formulation, a higher factor, or anything at all about performance. If you are holding a pack in a resort shop that says sunblock, you are holding a product from outside the UK and EU regime, or one whose labelling has not kept up.
The pool is not gentler than the sea
People treat a hotel pool as a softer environment than the beach, and in ultraviolet terms it is not. The water reflects, the surround is usually pale and reflects more, the shade is a parasol at the wrong angle, and sessions in and out of the water are long and repeated. The removal events are identical: immersion, towelling, reapplying rarely.
What is not verifiable
We do not publish ultraviolet index figures for destinations, because they change daily and we are not a forecasting service. Use the local meteorological service, or the World Health Organization's index bands with whatever local forecast is available. We also cannot tell you whether a specific pack bought abroad meets UK expectations, because we do not test products and never will.
Coming home
A fortnight in the tropics is a large, concentrated exposure, and holiday burns are the ones people remember years later. The NHS publishes guidance on sun safety and sunburn. If a burn blisters or you feel unwell, that is a call to a pharmacist or a GP. If something on your skin changes in the weeks after, that is a GP appointment. We give no diagnostic guidance here.