Most of what people call ageing skin is not age at all — it is sunlight, accumulated over decades.
Skin ages in two ways, and it helps to keep them separate. The first is intrinsic: the slow, genetically-scheduled process everyone goes through. Collagen production tapers, the skin thins slightly, fine lines appear. You do not control this, and honestly there is not much to be done about it beyond looking after yourself sensibly.
The second is extrinsic — damage from the outside world — and here one factor dwarfs all the others. Sun exposure is by far the largest external driver of how your skin looks over time. Pollution, smoking, and poor sleep all contribute, but ultraviolet light does more visible damage than the rest combined. Dermatologists have a name for the result: photoageing. It is the part of ageing you actually have a say in.
What UV does beneath the surface
Ultraviolet light comes in two forms that matter here. UVB is the shorter wavelength — it works on the surface and is what burns you on a hot afternoon. UVA is longer, and it is the one that ages skin. It penetrates deeper, down into the dermis where the structural proteins live.
Once there, UVA sets off a chain reaction. It generates free radicals — unstable molecules that damage cells — and switches on enzymes called matrix metalloproteinases. These enzymes break down collagen and elastin, the two proteins that keep skin firm and springy. Collagen gives structure; elastin lets skin snap back after it moves. Degrade both, year after year, and the skin loses its ability to hold its shape. Lines settle in and stay. UV also disturbs the cells that produce pigment, which is where uneven patches and sun spots come from.
The important word is cumulative. A single afternoon does little you will notice. The same dose, repeated across twenty summers, is written into the skin permanently.
What it looks like on a face
Intrinsic ageing tends to be gentle and even — soft lines, a general thinning. Photoageing looks different. It shows as mottled, uneven pigmentation, a leathery or roughened texture, deeper and more stubborn lines, a slightly sallow tone, and small broken capillaries. It concentrates exactly where the sun lands most: forehead, the tops of the cheeks, the nose, the ears, the back of the neck, and the hands.
There is a well-known illustration of this. People who spend years with one side of the face habitually turned toward a window — long-distance drivers are the classic example — often show markedly more lines and pigmentation on the exposed side. Same person, same age, two different rates of ageing, decided by nothing but sunlight.
The exposure you are not counting
Most men picture sun damage as beach holidays and burnt shoulders. That is UVB, and it matters, but the ageing damage is quieter and more constant than that.
UVA is present all day, all year, whenever there is daylight — not just when it is hot or bright. It passes through cloud, so an overcast sky is no real protection. It also passes through ordinary window glass, which blocks most UVB but lets much UVA through. The walk to the station, the desk by the window, the drive across town: none of it registers as sun exposure, and all of it adds up. This incidental, day-to-day dose does more of the long-term work than the two weeks you spend abroad.
What actually helps
The single most effective thing you can do to influence how your skin looks in twenty years is unglamorous: protect it from the sun, consistently. A broad-spectrum SPF worn daily — not just on holiday — does more to preserve the skin's appearance than any serum on the market. Broad-spectrum matters because it covers UVA as well as UVB; a high number that only guards against burning is missing the part that ages you.
Reapply if you are outdoors for any length of time, since it wears off. Shade and a hat in strong midday sun cost nothing and help. None of this reverses damage already done, and no product can — but it slows the accumulation of what comes next, and consistency beats any single clever product.
One caveat worth stating plainly: this is about appearance. If you notice a mole changing, a spot that will not heal, or any new mark that concerns you, see a GP or dermatologist rather than waiting. That is a different question from how your skin looks, and it is worth taking seriously.