By the Space Daily editorial team. This article is general science reporting, not personal medical advice. Readers with specific concerns about their skin or sun exposure should consult a qualified dermatologist or general practitioner.
Visit a small village in the south of Italy or the rural west of Ireland or a fishing town anywhere along the Mediterranean, and the same pattern keeps appearing. Two seventy-year-old women who grew up on the same street, who ate the same food, who married locally and stayed put, look like different generations. One has the deep crosshatched skin of a person who has spent a lifetime outdoors. The other looks fifteen years younger. The standard explanation, offered usually by the younger-looking woman herself if asked, is that she has been lucky with her genes. A more boring explanation, consistent with what the dermatology literature says happens at the population level, is that her mother kept her in the shade as a child, or she worked indoors, or she wore a wide-brimmed hat without thinking about it, or her job took her into a kitchen at 11am every morning of her adult life. No single anecdote settles which of the two it is in any given case. What the population-level evidence does say is that most of the variance in visible skin ageing, in lighter-skinned populations, comes down to one thing. The thing is sunlight, accumulated over decades, in doses too small on any given day to notice.
The figure most often quoted in dermatology, established in a 2013 paper by Frederic Flament, Roland Bazin and colleagues in Clinical, Cosmetic and Investigational Dermatology, is that “UV exposure seems to be responsible for 80% of visible facial aging signs.” That paper analysed 298 women in Montpellier in southern France, comparing clinical aging markers between sun-seeking and sun-avoiding cohorts in each decade of adult life. The 80% figure is a population-level estimate for lighter-skinned women, not an individual prediction, and it is consistent with a broader body of dermatology research going back through the 1980s and 1990s. The remaining 20% or so is what dermatologists call intrinsic ageing, the slow physiological process that would happen even if a person spent every day of their life underground. The two processes look different at the cellular level and produce different patterns on the skin, as set out in detail in the 2015 review by Laure Rittié and Gary Fisher of the University of Michigan in Cold Spring Harbor Perspectives in Medicine. Intrinsic ageing makes skin thinner, drier and less elastic in a uniform way. Photoageing produces the specific package most people recognise as “old skin”: coarse wrinkles, mottled pigmentation, broken capillaries, leathery texture, and the slightly translucent quality that comes from collagen and elastin underneath being replaced with disorganised, scar-like tissue.
What the strongest evidence actually shows
The cleanest piece of evidence on this question is a randomised controlled trial published in Annals of Internal Medicine in June 2013, with first author Maria Celia Hughes and senior author Adèle Green at the Queensland Institute of Medical Research in Australia. The data came from a larger long-running study called the Nambour Skin Cancer Prevention Trial, which had enrolled 1,621 adults from a single Queensland town in the early 1990s and followed them for years. Within that population, 903 people under the age of 55 were randomised in a 2×2 factorial design that compared daily sunscreen use against discretionary use, and beta-carotene supplements against placebo. For the photoageing question, the relevant comparison was the daily-sunscreen group against the discretionary-sunscreen group, with the supplement variable controlled for.
Participants assigned to the daily-sunscreen arm were asked to apply broad-spectrum SPF 15 to face, arms and hands every morning. Those in the discretionary arm were told to use sunscreen as they normally would, which for most Australians at the time meant occasional beach-day applications and not much else. Both groups were followed for four and a half years. Their skin was assessed by silicone moulds taken from the backs of their hands, graded by trained observers who did not know which group each participant belonged to.
The result was clean. The daily-sunscreen group showed no detectable increase in photoageing over the four and a half years of the trial. Skin ageing in that group was 24% less than in the discretionary-use group, with a relative odds ratio of 0.76 (95% confidence interval 0.59 to 0.98). The participants were under 55 when the trial began, the age band in which photoageing is still the dominant signal in skin changes rather than ordinary chronological ageing.
This is a strong finding and should be held in its proper context. The Hughes/Green trial used SPF 15, which is now considered low by current dermatological standards. It was conducted in a population with high background sun exposure (Queensland, latitude 26 degrees south) and consisting mostly of fair-skinned people of European descent. Whether the same effect size applies in populations with darker skin, or at higher latitudes, or with the higher-SPF products now widely available, is less clear. What is not in doubt, on the strongest available evidence, is the direction of the effect. Sun protection slows photoageing. Cumulative exposure produces it.
Why “good genes” is mostly the wrong answer
Genetics do real work in how skin ages. Melanin content, the primary genetic determinant of skin colour, also determines how well skin absorbs and dissipates ultraviolet radiation before it reaches the dermis. Higher melanin levels offer significant natural protection, which is why darker-skinned populations show photoageing differently and usually later. DNA repair efficiency varies between individuals. Genes governing collagen production, antioxidant capacity, and inflammatory response all contribute. Twin studies report heritability estimates ranging from roughly 40% to 70% for various skin-ageing traits, depending on which trait is measured. That heritability is real. It is also less than the whole story. A heritability of 60% on a given trait means roughly 40% of the variance is environmental and behavioural.
The trick is that the environmental and behavioural component is heavily weighted toward a single factor, and that factor accumulates so slowly that nobody experiences it as a decision. A child raised by a parent who covers their head at the beach is not making a sun-protection choice. A bookkeeper who spent forty years in an office building is not, in any meaningful sense, choosing shade. A person whose work hours happened to fall between 4pm and midnight has been protecting themselves from peak UV without ever framing it that way. The sun-protective behaviours that show up in someone’s seventies as smooth skin are almost always invisible to the person who practised them. They look, from the inside, like ordinary life. From the outside, decades later, they look like luck.
The contrary case is also true. The person who looks ten years older than they are often did not consciously choose to be photoaged either. They worked outdoors, or they lived through a phase of life when tanning was fashionable, or they had a job that put them in a car for two hours a day with the western sun coming through the driver’s window. The asymmetric photoageing visible on the left side of long-haul truck drivers’ faces in North America is a real and well-documented dermatological finding, most famously illustrated in a 2012 New England Journal of Medicine case by Jennifer Gordon and Joaquin Brieva of Northwestern University, showing a 69-year-old delivery driver after 28 years on the road. The cumulative dose did the cumulative damage. Nobody planned it.
What else matters, and why this article is about skin
The title of this piece talks about people seeming to age slower in general, which is broader than skin alone. Some honesty about that broader claim is necessary. Posture, body composition, energy, cognition, voice and movement all contribute to how old someone seems, and the science on those is more complicated. Smoking is the second-largest modifiable contributor to visible facial ageing, with effects on collagen and microvasculature that compound with sun damage rather than substituting for it. Sleep, alcohol, exercise, chronic stress, and diet all have measurable effects on various ageing markers, though usually smaller and with weaker evidence bases than the photoageing literature. The “mostly one thing” framing applies cleanly to visible skin ageing. It applies less cleanly, though still meaningfully, to the broader question of how old a person looks at sixty or seventy.
The single largest controllable contributor to the visible ageing of human skin, on the available evidence, is not a product, not a procedure, and not a recent discovery. It is the accumulated decision, mostly made unconsciously, about how much ultraviolet light the face has been allowed to absorb between the ages of zero and seventy. People who look young for their age have usually been making that decision in their favour, often without realising it, for fifty years or more. The dermatology literature has been clear on this point since the 1990s. Public knowledge of it is patchier, which is part of why it tends to read as luck.
For practical sun-protection guidance, the American Academy of Dermatology and Cancer Council Australia both publish authoritative public-health resources. Individuals concerned about specific skin changes should consult a qualified dermatologist.
