Say 'skin ageing' and most people think of the sun: UV, tanning, spots. So they wear sunscreen, carry an umbrella, wear a hat. All correct.

But there's a variable that rarely gets named: temperature itself. An epidermis held at elevated temperature for long periods ages faster — the idea is called heat ageing. It is a separate line from UV, and here is the awkward part: sunscreen blocks UV, not temperature.

A tan and heat ageing are two different things

A tan comes from UV. You see it immediately, and it fades. Because it's visible, people protect against it.

Heat ageing comes from temperature. Nothing shows at the time, and it doesn't fade — it accumulates. Because it's invisible, almost nobody guards against it. You can wear sunscreen all day while the heat side stays wide open.

It happens when you don't feel 'in the sun'

1. A bowl of hot noodlesFace over the bowl, steam rising straight into it. Ten minutes, no sun, and your face is being steamed.
2. Cooking over a high flameStanding at the stove, face less than a metre from the heat. For people who cook daily, it's a fixed block of high temperature every day.
3. Saunas, steam rooms, long hot bathsHeat you seek out on purpose. Pleasant — and for skin, a complete heat exposure.
4. The window side of your face when drivingSide-window glass stops most UVB, but some UVA and heat pass through. Long-haul drivers take both, on the same side, every day.
5. Rooms and commutes without air conditioningA stuffy kitchen, a rooftop room, waiting at a light under a scooter arcade. High temperature, and no moving air to carry it off.

Why it matters more here

Look at monthly mean temperature and draw a line at 25°C. Kaohsiung sits above it seven months a year; Taipei four, with May and October just short. Luxembourg never crosses it — its warmest month, August, averages 19°C.

Add humid air that slows sweat and slows cooling (covered in the sunscreen piece). So: in Europe you can talk about ageing and mostly mean the sun. Here, for several months a year, heat is the main character.

Running it through the four levers

1. Interval: step away from the heat, cool down, then touch your faceAfter noodles, cooking, a shower or the sauna, let your face come down first — ten minutes, or a pat of room-temperature water — then apply. Covering skin that is still hot seals the heat in.
2. Quantity: when you're hot, keep the top layer thinA heavy occlusive film on hot skin only makes the heat harder to shed. Go light for that round. The one exception is sunscreen before you go out — that layer is never reduced.
3. Timing: schedule care after the heat, not beforeIf you cook or take hot showers in the evening, do your routine after that and after cooling down.
4. Order: when you're hot, deal with sweat firstBlot the sweat before anything else. Sweat left on the face is a layer of water on top of the heat.

And the most direct move, which isn't a lever: put some distance between your face and the heat. Turn the extractor fan up, let the noodles sit a minute, don't lean over the pan, shorten the sauna, use a sunshade on the driver's-side window.

The idea of heat ageing, and the claim that prolonged elevated epidermal temperature accelerates ageing, are drawn from PuraVida, A Skincare Philosophy Born for Climate Adaptation. Quantitative research in this area is still accumulating; this site does not present it as settled, and does not claim any product reverses it. Monthly mean temperatures are ERA5 six-year averages, 2019–2024. This is not medical advice.

You can see a tan, so you guard against it.
You can't see heat ageing, so nobody does.
It doesn't need the sun. It only needs your face to stay in the heat long enough.