SPF, reapplying and makeup: Sunscreen questions answered

Caption:The average adult should use about seven to nine teaspoons of sunscreen for full-body and face coverage - about 1 teaspoon for each part. (file image)Photo credit:Unsplash / Fellipe Ditadi

As much as the monitoring is key for reassurance, how you store, apply and reapply sunscreen can be crucial to prevent skin damage and burning too.

Here’s what to know when you’re slopping on sunscreen this summer.

Note: Sunscreen also shouldn’t be your only defence against UV. Seek shade and wear a hat, sunglasses and protective clothing.

How should I store sunscreen? And what if it’s expired?

Dermatologist AJ Seine, president-elect of the NZ Dermatological Society, says don’t leave sunscreen sitting in a hot car or glove box.

“A hot car turns the active ingredients useless pretty fast.

“Stash it in a cool, shaded spot, like at the bottom of your beach bag wrapped in a towel.”

Expired sunscreen should be thrown out, he says, because “the emulsion breaks down, the filters degrade, and you are basically rubbing on false hope”.

How much sunscreen should I apply and how often?

University of Otago senior research fellow Bronwen McNoe, who sits on the sunscreen standards committee and has conducted research with funding from Cancer Society, says correct application and reapplication matter.

For the average adult, the guidance is about seven to nine teaspoons (or about 35g) for full-body and face coverage (not forgetting the top of your head if you’re bald), McNoe says.

“The amount you apply is much, much more important than whether it's SPF30 or 50, because if you don't apply enough, you're not going to get that good coverage.”

SPF50 filters about 98 percent of UVB compared with about 97 percent for SPF30. Both should be reapplied every two hours, McNoe says.

As Australian science communicator and cosmetic chemist Michelle Wong explains, the layer of sunscreen you apply naturally begins breaking and clumping up from sweat and the skin moving and producing oil. That film of sunscreen also gets thinner as it evaporates and absorbs on your skin over time.

Sunscreen should also be applied 20 minutes before going outside, McNoe says.

Why am I getting sunburnt while wearing sunscreen?

If you’re applying enough sunscreen and reapplying it correctly but still getting burnt, other factors may be involved.

Dermatologist Seine says some acne treatments, antibiotics, blood pressure medicines and even anti-inflammatories, such as ibuprofen, can make skin more sensitive to sunlight.

“Reflection off water, white sand, and concrete also dials up your UV exposure, and water resistance claims only buy you about 40 to 80 minutes before you are bare again.”

Seek advice from a health professional if you’re concerned about changes in your skin.

What if I have a tan or darker skin?

McNoe’s recent survey found a quarter of New Zealanders believed a suntan protected against melanoma – which is not true. A fake tan also doesn’t provide sun protection.

“A base tan only provides an SPF of about four, so very, very low… a base tan anyway is a sign of skin damage and any UV can potentially damage your DNA, not just [cause] a sunburn.”

People with darker skin are at lower risk of skin cancer, but are not risk-free and should still use sunscreen and other sun-protection methods, McNoe says.

At what UV index should I use sunscreen?

Sun protection should start at UV index 3, McNoe says, so don’t let clouds or cooler temperatures fool you.

Experts generally advise sunscreen between 10am and 4pm, particularly from September or October until April.

Can your skin be damaged without sunburn?

Yes. Dermatologist Amanda Oakley previously told RNZ that skin accumulates damage from sun exposure, making UV protection important from a young age and as people get older.

"Skin cancers are very prevalent and the population is ageing, and as most skin cancers occur over the age of 65, and now 65-year-olds are regularly living until 95, and the epidemic of skin cancer has become horrendous, especially in white-skinned people [who are at more risk]," Oakley says.

“You can go outside for just a few minutes when you're older and think 'that's all right, I didn't get burnt'. But what's happened is the long-wave ultraviolet has increased that immune suppressant effect of age. And you might have got a dormant skin cancer and then it sprouts because of just those few minutes outdoors and your age."

Are spray and stick sunscreens as good as lotion?

The formula isn’t necessarily the problem, dermatologist Seine says. Getting enough of it onto your skin can be.

“You would need about four to six seconds of spraying per limb, rubbed in, to get the stated bottle rating.”

Aerosol sprays may be worse. In 2021, Australian research found between 28 and 93 percent of sunscreen from five tested aerosol sprays was lost in 20km/h winds, and 32-79 percent when the winds dropped to 10km/h.

“A person would need to spray on aerosol sunscreen in some cases for up to 250 seconds per limb or more than a bottle’s worth to provide adequate protection for a whole body application,” said Elke Hacker, a senior research fellow at Griffith University.

Seine says sticks are great for ears and under eyes, but you have to swipe about four times over the same spot to get full coverage.

That’s why lotions remain the most reliable option, he says.

What about SPF in foundation and BB creams?

Again, the difficulty is applying enough to achieve the stated SPF.

Seine says you would need seven to 10 times the normal amount of foundation to reach its labelled SPF.

In her blog and video on SPF in makeup, Lab Muffin Beauty Science’s Wong says sun protection scales with the amount you apply. So if you’re only applying half of the makeup SPF required then you’d only get half protection on the label.

How do I apply and reapply sunscreen with makeup?

Seine says sunscreen should be the last step of skin care and first step in makeup. Apply a dedicated broad-spectrum SPF50 sunscreen first, letting it sink in for five minutes, then do your makeup.

Some people use a makeup cushion applicator to reapply sunscreen over makeup, Wong says, although transfer of coloured makeup can be a problem.

“If you’re getting a ton of sun, I would just give up on trying to save the make up,” Wong says in her video. “To get a really solid reapplication, you should just reapply your regular sunscreen normally and then redo the make up on top.”

Wong also advises making sure the ingredients in sunscreen and makeup are compatible, although she says the impact may be low.

Is expensive sunscreen better?

Not necessarily.

Dermatologist Oakley previously told RNZ the most important consideration is whether you like a sunscreen enough to actually use it.

"The cost might be more of a marketing ploy [rather] than an effectiveness of the product ... but it may be more expensive to produce something that people find cosmetically acceptable.”

Consumer NZ’s testing has also found no evidence that more expensive sunscreens provide better protection.

If I’m covered up, do I still need sunscreen?

If long sleeves and trousers will stay on, sunscreen is only needed on exposed skin, McNoe says.

But if you’re likely to remove clothing or a hat later, apply and reapply sunscreen to those areas as usual, she says.

What about children?

McNoe says sunscreen shouldn’t be used on babies under six months. Instead, keep them out of the sun and use sun-protective clothing and hats.

After six months, she recommends doing a patch test to check for a reaction.

Dermatologist Seine says mineral formulas can be gentler on children’s skin, which is thinner, absorbs chemicals more easily and gets irritated faster.

“For toddlers, turn applying it into a game or use a foundation brush to paint it on their face so it does not feel like a wrestling match.”

What are mineral and chemical sunscreens?

Physical or mineral sunscreens contain ingredients such as zinc oxide and/or titanium dioxide, traditionally understood to reflect UV radiation. However, research shows they also absorb UV light, much like chemical sunscreens. Some products listed in Australia as “mineral-only” have also been found to contain chemical ingredients.

Chemical sunscreens generally use ingredients such as octinoxate, avobenzone and homosalate to absorb UV radiation and convert it into heat. An Australian pharmacologist previously told the ABC there are a host of new chemical ingredients that can’t be absorbed through the skin into our cells.

McNoe says there’s no difference that we know of between the two in terms of efficacy.

How can I tell if the SPF claim on my sunscreen is true?

While the Sunscreen (Product Safety Standard) Act 2021 requires sunscreens to be independently tested, there is no requirement for regular retesting. A product may therefore rely on testing from several years ago.

Consumer NZ’s database covers more than 160 sunscreens. This year, nine listed products relied on testing more than 10 years old, while many others relied on results from five to 10 years ago. Another 36 had no testing information available.

Several manufacturers, including Beiersdorf (Nivea), Edgewell Personal Care (Banana Boat and Hawaiian Tropic) and Neutrogena, declined to provide any information.

Speaking to RNZ previously about Korean and Japanese imported sunscreens, Consumer NZ researcher and writer Belinda Castles recommended looking for products that explicitly state they comply with A/NZS and asking retailers for evidence when in doubt.

What if my sunscreen failed SPF testing?

McNoe says she wouldn’t recommend relying on a product that tested as low as SPF14, but SPF30 still provides adequate protection, filtering about 97 percent of UVB rays.

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