Published on bearblog

To Escape the Heat, Just Apply Suncream?

Recently there have been several spells of unusually hot weather in the UK (including one day in July with a temperature of 41 degrees Celsius, substantially above the previous record of 37 degrees). As you would expect, the media has been full of advice about how to deal with the unusual heat.

Invariably the advice includes many sensible ways to cope, like staying in cool places, drinking water, wearing less clothing, etc. But there’s usually another bit of advice provided. To wear suncream.

Here’s what the BBC says1:

If you do have to go outside, wear a sunhat and sunscreen and try and stay in the shade where possible

And the Guardian2:

Not everyone will be able to hunker down indoors. But precautions are necessary if venturing outside. Wear light, loose-fitting clothes, sunglasses, sunscreen and a hat, take water with you, and try to stick to the shade.

And even the Met Office3:

Walk in the shade, apply sunscreen and wear a wide-brimmed hat, if you have to go out in the heat.

There is just one problem with this last piece of advice. It’s wrong. Hot weather doesn’t cause sunburn. There are only three controllable factors4 that affect sunburn incidence: the UV strength of sunlight at the time of exposure (UV index), time spent outside, and the skin’s preponderance to burn (natural, as modified by protective clothing or suncream). The outside temperature does not feature among these three factors.

Of course, correlation does not equate to causation, and undoubtedly the statistics will show that serious sunburns correlate well with periods of hot weather. More people will go outside more often and for longer when the weather is hot; and this will result in some small percentage of sunburnt people, vaguely proportional to the increased time spent outside.

But the hot weather did not cause the sunburns! The people that got burned all did so for mundane reasons - perhaps they forgot their hat or to apply suncream; misjudged how long they could stay outside, went outside at midday when the sun is strongest rather than in the morning or evening, or any one of many other similar reasons. The sun would have been just as dangerous if the day had been cooler.

That said, the correlation is valid, and a cause for concern: sunburns damage the skin and are believed to cause serious cancers. If sunburns are more common during hot weather then finding ways to reduce sunburns during hot weather is a valid public health objective. It is just that the correlation is only relevant at the population level - for an individual the heat outside is irrelevant to how they should approach sun exposure.

Indeed I suppose if you asked the question directly - “does hot weather cause your skin to burn or not?”; few people would say that it does. As is common sense: one does not get sunburn from sitting in a sauna, or working in a hot kitchen, or any other time one is hot. There is nothing different between those occasions and the same heat, but outside. Nevertheless the advice’s memetic value persists, and one is often reminded by well-meaning peers and authority figures: “It’s hot, don’t forget to wear your suncream!”.

My concern is that by over-emphasizing sun protection advice during exceptional circumstances like a heatwave, the importance of sunburn awareness at other times is diminished in the collective consciousness. In the UK, you can pick any day in the four months between May and August and the it’s likely that the midday sun will be strong enough to burn a large proportion of the population. Sun awareness is an everyday action, not something to be reserved for exceptional circumstances like the one major heatwave a year.

Perhaps we can adjust the wording of our collective advice - from “It’s hot, don’t forget to wear your suncream!” to something more like “don’t stay out in the sun too long - apply sun protection as usual, proportional to your exposure!”

Footnotes:

  1. original article on the BBC 

  2. original article on the Guardian 

  3. original article on the Met Office website 

  4. I say three, but there’s really just one factor that affects sunburn - the amount of UV-mediated damage caused to your skin. But one can’t control that directly, only by controlling other factors can one control the real cause of sunburn. 

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