Why do you sunburn easier at high altitudes?

At higher altitudes, the air is cleaner and the atmosphere thinner. This causes the sun to be stronger. But this is exacerbated by snow cover and the fact that it's colder and therefore less noticeable.

Sunburn in the spring and summer: most people are quite familiar with this. The cause lies in the strong sun and part of its radiation: UV-A and UV-B. These are present to a much greater extent in spring and summer than in winter, when they are largely absent.

It is no surprise that the sun’s power is much bigger in summer than in winter. The sun is higher in the sky and therefore shines into the atmosphere at a right angle. More energy is delivered per square meter, because the angle is smaller.

In winter, the sun is lower in the sky. As a result, sunlight spends a greater part of its journey through the atmosphere, which absorbs much of the UV light. In fact, the most harmful sunlight, UV-C, is almost completely absorbed by the atmosphere. But in the mountains everything changes. How does this work?

UV light in the mountains

In the mountains, the effect of UV light is no different than at sea level. But the effect does occur faster: there is a smaller atmosphere above you that can absorb the radiation. Although ozone (in the ozone layer) absorbs a large part of UV light, the other gases in our atmosphere also play a role in absorbing UV radiation.

With every thousand meters you ascend, UV intensity increases by 10%, according to WHO data. This is an important fact: at 3,000 meters the amount of UV radiation is therefore 30% more than at the same location at sea level.

At a great height, however, something else plays a role: reflection. The higher you go, the colder it gets, but that’s not because the sun’s energy is smaller. Getting colder has everything to do with the expansion of air, not the sun’s intensity.
However, getting colder has a different influence: snow cover or glaciers are more common. Fresh snow reflects almost 100% of the light. This effectively gives you almost a double dose of light: you burn considerably faster.

Because it is colder, you will notice this less quickly. A possible breeze will even make sure you don’t notice it at all. That can be dangerous; combustion is imminent.

Another effect is the fact that this radiation comes from below, and not from above. The underside of your face normally hardly gets to endure direct sunlight. This is the case above the snow.

Tips to prevent sunburn

Applying sunscreen (with a high protection factor and water-resistant) is an obvious way to protect yourself against the sun. But don’t forget your sunglasses either: the human eye cannot withstand the large amount of light, but rubbing is obviously not an option.

It is also advisable to keep arms and legs covered if the weather permits. This is a trade-off between comfort (in terms of warmth) and protection.
Last but not least: avoid the highlights of the radiation. The radiation is strongest between roughly 12 and 16. Before and after that, the radiation is less strong, because the sun is lower in the sky. This does not necessarily coincide with the hottest time of the day, which in summer is often only measured between 4 and 6:30 pm.

If possible, plan the trip so that you are not at the highest point of the day, or on a glacier at the peak of the day. In any case, the latter is not pleasant: the top layer becomes soft and mushy, which makes walking difficult. A trip through a wooded area in the middle of the day significantly reduces the risk of burning.

Don’t be fooled by clouds. Thin veil clouds contribute almost nothing to UV filtering, and a partly cloudy sky can even provide more radiation thanks to the reflection from the high clouds.


Plan your trip wisely: avoid snowfields in the afternoon and preferably look for a forest
Lubricate yourself! Also at the bottom of your face
Wear a hat or cap and sunglasses
If pleasant: long sleeves (thin sweater) and long pants protect the limbs

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