Sun damage is four problems, and one is not cosmetic.

Yes, in layers. Stopping the dose lets the skin repair: in the one-year sunscreen study every subject improved, with texture and pigmentation 40–52% better. Retinoids reverse the biology — collagen restored on biopsy, wrinkles and mottling reduced in eight randomised trials. Light and lasers remove the colour that sun switched on; ablative resurfacing removes the elastotic surface and grows a new one; fluorouracil and photodynamic therapy clear the precancerous field. What none of them reverses is the mutated clones in the cells that remain, which is why sun-damaged skin stays a cancer risk after it looks better, and why the yearly look is part of the treatment.

The Nambour trial that cut carcinomas and melanomas used an SPF 15–16 sunscreen applied daily, and the one-year reversal study used SPF 30. The difference between 30 and 50 is small if both go on generously; the difference between a generous layer and the thin smear most people use is large, because SPF is tested at an amount few reach. So: broad-spectrum, SPF 30 or above, roughly half a teaspoon for the face and neck, every morning regardless of weather, carried to the ears, chest and backs of the hands, reapplied after two hours outdoors or after sweating, and a tinted iron-oxide formulation for anyone whose complaint is melasma or spots. The best sunscreen is the one you will use every day.

UVA — the wrinkle wavelength — passes through ordinary window glass and through cloud, which is why the office worker by the window and the driver on the window side photoage on one side. Vehicle measurements found side windows blocking 89% of UVA against the windscreen's 99%, a more than tenfold difference in what reaches the driver's cheek and forearm; a UV film closes the gap. Winter sun in northern Europe carries little UVB, so it rarely burns, but the UVA that ages skin varies far less through the year. Deep indoors away from windows, the dose is negligible and sunscreen is optional; beside a window, on a commute, on a cloudy walk, it is not.

The honest answer changed in 2025. The older trial with SPF 17 found no effect on vitamin D; the Sun-D trial with daily SPF 50+ found a real but small one — a 5.2 nmol/L smaller rise over a year and deficiency in 45.7% of daily users against 36.9% of controls — and concluded that regular users may need a supplement. The arithmetic is simple: 1,000–2,000 IU of vitamin D a day costs a few euros a month and carries no mutations; the ultraviolet dose needed to make the same vitamin in skin is the dose this page exists to prevent. Use the sunscreen, take the tablet, and get the level checked if you are indoors most of the year anyway.

A rough, scaly, pink or skin-coloured patch on sun-exposed skin that flakes off and returns in the same place is almost always an actinic keratosis, the visible tip of a mutated field. Individual keratoses regress about a quarter of the time; the field does not, and the interval from a keratosis to a carcinoma at the same site averaged about two years in the kinetics analysis, with a lifetime risk of roughly 6–10% for someone carrying them. A single lesion is frozen; several mean a field treatment — a course of fluorouracil cream, which also cut carcinomas needing surgery by 75% in the veterans' trial, or photodynamic therapy — and a yearly check afterward. A patch that thickens, bleeds, hurts or crusts is seen this month, not next year.

A tan is the skin's response to ultraviolet injury — melanocytes producing pigment because DNA has been damaged — and the protection it gives is about an SPF of 3, which no dermatologist would sell you in a bottle. Sunbeds deliver UVA at intensities the sun does not: first use before 35 raises melanoma risk by 75% in meta-analysis, and the devices are classed as carcinogens. Self-tanning lotions colour the dead outer layer with a sugar reaction, involve no ultraviolet, and are the only tan this page endorses; they do not protect, so the sunscreen goes over them.

Melanin absorbs much of the ultraviolet dose, so darker skin burns rarely, keeps its texture longer and grows far fewer keratinocyte cancers. Its sun problem is pigment: melasma and dark patches triggered not only by ultraviolet but by visible light, which produced darker and longer-lasting pigmentation than UVA in darker phototypes and which only iron-oxide-tinted sunscreens block. The devices on this page carry more pigment risk in Fitzpatrick IV–VI, which is why the non-ablative lasers and lower settings are the rule and why the dark-spots guide exists. Melanoma is rarer but deadlier because it is found late — on palms, soles and under nails, where sun is not the cause and nobody looks; any new dark streak or spot there is a dermatologist's appointment.

Everything here works through repair, and repair is slow. Daily sunscreen showed measurable improvement in the one-year study from week 12 and kept improving to week 52. Retinoids change the surface over three to six months and the dermis over a year; the tazarotene trial was still improving at week 52. Intense pulsed light and Q-switched lasers darken spots for a week before they flake, and colour is judged at a month after each of three sessions. Fluorouracil and photodynamic therapy are red and raw for one to four weeks and smooth at six. Ablative resurfacing is pink for weeks and judged at three months. Photograph in daylight before anything, and again a year in.

The ladder in euros: sunscreen, a three-inch brim and a vitamin D tablet (€15–40 a month, the only rung with cancer-prevention trials) → a prescription retinoid or adapalene (€10–30 a month, the class with the photodamage trials) → vitamin C and niacinamide under it (€15–60 a month) → a yearly skin check for anyone with a field (€80–200) → fluorouracil for the field (€20–60 a course) or photodynamic therapy (€900–1,300) → intense pulsed light or a Q-switched laser for colour (€600–1,500 for a course) → non-ablative fractional laser or a medium peel (€150–600 a session) → ablative resurfacing for the leathery face (€800–3,500). Oral photoprotectants, nicotinamide for the high-risk and self-tanner sit beside the ladder; sunbeds sit under it.

Photoaging is cumulative and mostly incidental, so prevention is a habit rather than a purchase. The trial-proven habit is daily broad-spectrum sunscreen on the face, neck, ears, chest and hands, every morning, in every season, reapplied when outdoors — the Nambour cohort cut its carcinomas, melanomas and measured aging with exactly that. A three-inch brim and shade between eleven and three cut the rest; a film on the car's side windows removes the driver's asymmetry; sunbeds are the one thing on this page with no safe dose. A retinoid from the late twenties rebuilds what slips through, and vitamin D comes from a tablet. The 30s guide covers the decade, and the inner-arm test will tell you at fifty how well it worked.

Sun-damaged skin is a cancer field, and the cosmetic treatments on this page are safe only on skin that has been looked at. Actinic keratoses progress to squamous-cell carcinoma at rates that vary by study but average about two years per event in the kinetics analysis (kinetics study), with a lifetime risk for someone carrying them of roughly 6–10% (progression review); squamous-cell carcinomas on the ear, lip and scalp are the ones that spread. Melanoma's warning signs are asymmetry, an irregular border, more than one colour, a diameter over six millimetres and any evolution — and the lentigo maligna type looks like a sun spot for years (DermNet). The red flags for a keratosis: thickening, bleeding, tenderness, a horn or crust, failure to heal in a month (warning signs). A laser or light clinic that treats spots without a dermatoscope is treating blind; ask who looked first.

Sunscreen's harms are small and specific. The vitamin D effect is now measured: a year of daily SPF 50+ produced a 5.2 nmol/L smaller rise in vitamin D than discretionary use and left 45.7% of daily users deficient against 36.9% of controls (Sun-D trial) — a supplement costing pennies replaces it, and the 1995 trial with SPF 17 found no effect at all (1995 trial). The commoner failure is dose: the trials that prevented cancer used enough product to coat the skin, and most people apply a fraction, so the SPF on the label is rarely the SPF on the face. Filters are regulated on both sides of the Atlantic; mineral zinc and titanium suit reactive skin, and tinted iron-oxide formulations add the visible-light protection that pigment-prone and darker skin needs (iron-oxide study). Any sunscreen used is better than the best one left in the drawer.

Machines that target melanin and haemoglobin injure the cells around them when the settings or the skin type are wrong. Post-inflammatory hyperpigmentation follows intense pulsed light, lasers and medium peels far more often in darker skin, which is why the non-ablative devices and lower settings are the rule there; repeated low-fluence laser toning has produced permanent confetti-like hypopigmentation (JCAD); the randomised IPL trial recorded one atrophic scar in 32 patients and three withdrawals for pain (JAMA Dermatology RCT); and the neck, with few follicles to heal from, has scarred after fractional CO₂ at settings the face tolerates (neck scarring). Treated skin is photosensitive for weeks and re-pigments in sun; a course of light in June without sunscreen is a course of light wasted. The laser guide covers the settings by skin type.

Indoor tanning delivers UVA at intensities the midday sun does not, and the epidemiology is settled: a meta-analysis of seven studies found first use before age 35 associated with a 75% increase in melanoma risk and any use with a 15% increase, and the World Health Organization classes the devices as carcinogenic (indoor-tanning review; JEADV 2025). The "base tan" sold as protection is the skin's response to injury and shields about as much as an SPF of 3; the melanoma risk from tanning is highest in exactly the young, fair users who buy it. Every treatment on this page — the retinoid, the light, the laser, the field therapy — is undone by a sunbed, and a clinic that offers both is not reading its own literature.