Altitude, snow and cold: what actually happens to your skin outdoors

There is a kind of day on which people reliably burn without seeing it coming: cold, windy, maybe overcast, somewhere high up. Not a single signal your brain associates with sun, and yet the exposure is higher than on a warm day at the coast.

That is because the things that amplify UV have nothing to do with temperature.

What multiplies your exposure

Altitude

For every 1,000 metres of elevation, UV radiation increases by roughly ten per cent. The atmosphere above you is thinner and filters less out. At 2,500 metres, an ordinary ski altitude, you are around a quarter higher than at sea level.

Reflection

What lies beneath you counts. Fresh snow reflects up to eighty per cent of UV, which almost doubles your exposure. Sea foam does about twenty-five per cent, sand about fifteen, and water, grass and soil stay under ten.

Reflection comes from below, where a cap does nothing. It is why skiers burn under the chin and inside the nostrils.

Cloud

Thick cloud dampens UV. Thin or broken cloud barely does, and can locally raise the level because light scatters around the cloud edges. "It is overcast" tells you very little.

Windburn does not exist

This is the misunderstanding that does the most damage, because it points people at the wrong solution.

Wind does not scour your skin red. What we call windburn is sunburn, sustained on skin already weakened by cold and wind. Two things happen at once:

• Cold and wind break down your barrier. Cold air holds far less moisture than warm air, which speeds up evaporation from your skin. Wind adds to it by blowing away the humid layer of air just above the surface. What remains is skin with a depleted lipid layer: drier, more sensitive and more permeable.
• Cold numbs the warning signal. The stinging by which you normally notice you are burning is much less perceptible at low temperatures. You notice once you are inside and warming up, and by then the damage is done.

The practical consequence matters more than the terminology: a thick protective cream only half helps here. What actually counts is sun protection, including when it is freezing.

Cold, wind and your skin barrier

Your outermost layer works as a wall of cells with lipids between them, among them ceramides, cholesterol and fatty acids. That in-between layer keeps water in and irritants out.

Outdoors in the cold you lose that layer faster than you rebuild it. You notice it as tightness, flaking, red patches and skin that suddenly reacts to products that were always fine. That is not skin that has become sensitive, that is a damaged barrier.

Repair goes through lipids. A watery serum on a broken barrier simply evaporates. Ceramides, squalane and emollients do the work here.

Pollution counts too

Particulate matter, ozone and nitrogen oxides settle on your skin and generate free radicals there, which contributes to oxidative stress, collagen breakdown and pigment formation.

UV and pollution also reinforce each other: together they produce more oxidative load than the sum of the two. That is why an antioxidant under your SPF is worth having. The article on vitamin C covers that side.

A routine that fits this

Before you go out

1. Cleanse gently. Do not degrease before heading into the cold. Radical Refresh does not leave skin tight.
2. Antioxidant. Protective Power catches the free radicals that UV and pollution generate.
3. SPF, generously. Daily Defense with broad-spectrum SPF 30, about a quarter teaspoon for your face, twenty minutes before you leave. Do not forget ears, neck and the underside of your chin, because that is where reflection lands.

While you are out

Reapply every two hours, and more often if you sweat or wipe your face. Take a lip balm with SPF too, because lips have almost no pigment to defend themselves with.

Afterwards

Cleanse it all off, then repair rather than treat. Hydration Hero with Ceramide NP and squalane works on the barrier. Skip your acids and retinol that evening if your skin feels tight. You lose nothing by waiting a day.

Frequently asked questions

Do I really need SPF in winter?

UVB drops considerably in winter, UVA far less. Outdoors in snow or at altitude it is more urgent than in summer at the coast. What the SPF number itself means is covered in the article on SPF.

Why do I burn under my chin?

Reflection from below. Snow and water bounce UV back onto places that are normally in shade: under the chin, inside the nostrils, under the brows.

Is a thick cream enough against cold and wind?

For the barrier it helps, against UV it does not. You need both, and most rich winter creams contain no filters.

My skin flakes after a day outdoors. Should I exfoliate?

No. Flaking here means a damaged barrier, and exfoliating makes it worse. Repair first with lipids and hydration, and the flaking resolves on its own.

Sources

• World Health Organization, Radiation: Ultraviolet (UV) radiation, factors affecting UV levels.