New Zealand sun and skin ageing: what the evidence actually supports

The short answer

The UV in New Zealand is stronger than the UV in Europe at the same latitude. That is not a marketing line. Atmospheric scientists have measured it.

And the thing with the best evidence behind it for slowing the appearance of ageing is also the least interesting thing on any shelf. Daily broad spectrum sunscreen, applied generously and topped up. Actives come second. They are worth using, but they are second.

Why the UV here is stronger

When researchers compared summer UV-B measured at European sites with New Zealand sites on comparable latitudes, the European readings were up to 50 percent lower (Seckmeyer et al., 2008). Read that direction carefully, because it often gets flipped. The finding is that Europe is darker, not that we are 50 percent brighter.

The same team pulled the spectra apart to work out why. They put the gap down to four things: total ozone overhead, cloud, aerosol loading in the air, and the distance between the sun and the Earth, which is at its smallest during our summer rather than theirs.

Earlier New Zealand work calculated ground level UV running about 13 percent higher than at similar northern hemisphere latitudes, with peak summer intensity landing near 1.30pm local time (McKenzie and Elwood, 1990). Daylight saving is part of why the peak is that late. In summer our clocks put the middle of the solar day closer to half past one than to noon.

Those numbers were calculated from satellite ozone data in 1990, so treat them as the shape of the thing rather than today's exact figures. The geography point has held up better than any single number. That same work found UV drops only 5 to 10 percent between Auckland and Central Otago. There is no cooler, safer half of the country. The whole place sits in one strong band.

UVB burns. UVA is the quiet one

UVB is the sunburn wavelength, and ordinary window glass stops most of it. Much more UVA gets through, and UVA is around all day and all year, including in winter and on grey days.

There is an often quoted study on this. Ten people who already had noticeably more sun ageing on one side of the face, from years of exposure through a window, had both sides measured. The exposed side scored worse for wrinkles, was rougher across the cheek, and was more uneven in tone on the cheekbone (Mac-Mary et al., 2010).

Be honest about what that is. Ten people, no control group, and they were recruited precisely because they already looked asymmetrical. It cannot tell you how common this is or how much of the difference the window caused. It is a demonstration, not proof. It is still a fair prompt to think about the commute and the desk by the window.

This is the argument for broad spectrum rather than a big SPF number on its own. SPF measures protection against sunburn, which is mostly UVB. A separate test sits behind a broad spectrum claim, so that is the wording to look for on the label. A daily moisturiser with UVA and UVB protection, like Advanced Day Ultimate Protect, is one way to make that automatic on the days you are not planning to be outside at all. Check the SPF and the broad spectrum wording on the box of whatever you buy, ours included, because the number is what you are paying for.

What the sunscreen evidence actually says

The strongest trial is the Nambour study. Adults were randomly assigned to apply broad spectrum sunscreen daily or to use it at their own discretion, then followed for four and a half years, with assessors who did not know which group anyone was in. The daily group showed no detectable increase in the measured signs of skin ageing over that time, and 24 percent less than the discretionary group (Hughes et al., 2013).

Two caveats, because this one gets over quoted. It ran in subtropical Queensland at latitude 26 south, not here. And the outcome was skin surface microtopography, a texture measurement, rather than an overall judgement of how someone's face looked. The authors also noted missing data and modest power to pick up moderate effects. It is still the best evidence we have found on the question.

A one year randomised trial pointed the same way. Two hundred and ninety Brazilian women aged 30 to 65, across skin phototypes II to VI, either carried on with their usual routine or replaced their usual product with a high protection sunscreen used twice daily. Fifteen dermatologists graded wrinkle and pigmentation signs from standardised photographs (Flament et al., 2023). Signs of ageing increased in both groups over the year. They increased less in the sunscreen group, and for four of the eight signs the difference was statistically significant. Nobody went backwards.

Worth knowing about that one. There was no dummy product, so the comparison is against normal life rather than against an identical cream without filters, and the authors work for the company that makes the sunscreen they tested. The reason we have included it anyway is that it covered skin phototypes II to VI. Most of this research has been done on fair skin, and this is not advice for fair skin only.

How much you apply beats the number on the bottle

SPF is tested in the lab at 2 milligrams per square centimetre. Sunbathers apply roughly a quarter of that. When researchers put four different amounts of an SPF 4 sunscreen on the backs of 20 volunteers and measured what each thickness actually delivered, protection fell away steeply as the layer thinned (Faurschou and Wulf, 2007). It was one low SPF product on 20 people, so do not treat the exact maths as gospel. The direction is not really in dispute.

In practice, a generous layer of SPF 30 topped up at lunchtime does more for you than a thin smear of SPF 50 put on once at eight in the morning. On a New Zealand summer day outdoors, reapply every two hours, and again after swimming, towelling off or heavy sweating.

A few label notes for shopping here. Sunscreens sold in New Zealand have to meet the Australian and New Zealand sunscreen standard, which sets how SPF is tested and what a broad spectrum claim has to demonstrate. The highest number allowed on a label is SPF 50+, and the step up from 50 is small anyway. Nothing is waterproof. Water resistance is tested for a stated number of minutes, which is why that number is printed on the pack.

Sunscreen is not the whole job

Sunscreen is the part people buy, so it is the part that gets talked about. It is not the strongest tool you have.

• Shade and a wide brimmed hat in the middle of the day do more than any bottle, and they do not wear off.
• Sunglasses cover the eye area, which is where people run out of patience with sunscreen.
• Standard New Zealand sun safety advice is to protect yourself from September through April, especially between 10am and 4pm, and any time the UV index is 3 or above. The UV index forecast is free and it is worth a look before a day out.
• Clothing that stays on beats sunscreen you have to remember to reapply.

The two actives with vehicle controlled trials

Beyond sunscreen, two ingredients have been tested against their own base formula in human trials, which is a bar most ingredient claims never clear.

Retinol

In a randomised, double blind trial, 0.4 percent retinol was applied up to three times a week for 24 weeks to one arm, with the plain base cream on the other. The retinol side improved on fine wrinkling scores (Kafi et al., 2007).

The fine print matters here. It was 36 residents of retirement facilities with a mean age of 87. It was forearm skin, not faces. Study staff did the applying, so nobody missed a week. And it looked at naturally aged skin rather than sun exposed skin, which is the opposite of the topic of this article.

Retail products also vary enormously in strength, and a product does not inherit a trial result by having the word on the box. To put numbers on it, the Intelligent Retinol Smoothing Night Cream we stock is 0.2 percent retinol in a slow release form, which is half the concentration used in that trial and delivered differently. We sell it as a gentle starting point for people new to retinol, not as the product that was tested.

Niacinamide

Five percent niacinamide was applied twice daily to one half of the face, with its own base formula on the other half, for 12 weeks. The niacinamide side improved on the appearance of fine lines and wrinkles, yellowing and elasticity measures (Bissett et al., 2005).

Fifty women, all of them white, in a study run by researchers employed by a skincare manufacturer. The split face design is a genuine strength, since each person acted as her own comparison. The effects were real and they were modest. Nobody in that trial got a new face.

Using actives safely in this much sun

This part gets left out of most articles, and it matters more here than in most countries.

• Retinol goes on at night. Use sunscreen the next morning, every morning, without exception.
• Exfoliating acids, the AHAs in particular, can make skin more sensitive to sunburn. That sensitivity carries on for about a week after you stop. Daily sunscreen is not optional alongside them, and a New Zealand summer is a sensible time to ease off rather than ramp up.
• Start slowly with either. Two nights a week for a few weeks, then build. Redness, stinging, flaking or tightness means back off, not push through.
• Do not start a new active the week before a beach holiday, a wedding or anything else where you need your skin to behave.
• Patch test on a small area first, especially if your skin reacts easily.
• If you are pregnant or breastfeeding, talk to your doctor, midwife or pharmacist before using a retinoid.
• One new product at a time. Layering three actives at once tells you nothing about which one your skin liked.

What none of this can do

• It cannot undo past sun exposure. The sunscreen finding was that daily use slowed the increase in visible ageing. That is not the same as reversing anything, and we are not going to pretend otherwise.
• None of it is medical treatment. Nothing we sell treats a skin condition, and we will not say it does. If a spot or a patch of skin is changing, bleeding or not healing, that is a doctor's appointment, not a beauty counter.
• Supplements did not do this job. In the same trial that found the sunscreen benefit, beta carotene supplements had no overall effect on skin ageing, though the authors said more study was needed before ruling benefit or harm in or out (Hughes et al., 2013). We have kept this article to topical evidence, so oral collagen is simply out of scope here rather than judged.
• Screens are almost certainly not the problem. We have not seen good evidence that light from a laptop or phone changes how skin looks. Some products are marketed on blue light. That marketing is ahead of anything we can point you to.
• No product is formulated for New Zealand UV. The atmospheric research describes the sky, not any bottle. A good broad spectrum sunscreen is a good broad spectrum sunscreen wherever it was made.
• These studies tested ingredients, not our range. Not one product we sell was the product used in any trial above.

Where to start

Start with the boring thing. A broad spectrum sunscreen every morning, a proper layer of it, topped up when you are outside. Add shade and a hat in the middle of the day, because peak UV here lands around half past one, not at noon. Then, once that is genuinely a habit, add one active and give it three months before you judge it.

If you want a hand working out where to begin, come and talk to us in Parnell. We would rather talk you out of a shelf full of products than sell you one.