Mineral sunscreens are big news in SPF in 2017, with new releases from trusted brands such as Neutrogena, Ombrelle, Avène, Bioderma and La Roche-Posay. But along with the positive – more options, especially for those with sensitive skin – comes a big negative. A new nugget of advice is making the social-media rounds: a drop or two of facial oil mixed in with your titanium dioxide sunscreen will make it nicer to apply.
DON'T DO IT. DO NOT. DANGER, DANGER!
Sure, some titanium-dioxide or titanium-dioxide+zinc-oxide formulas are off-puttingly chalky, or leave that annoying white cast on your skin. A drop of serum or oil or moisturizer and maybe a drop of foundation will improve the texture, application and finish. But with that immediate payoff comes a danger that isn't so evident: compromised efficacy.
Putting serum, oil or foundation or anything into sunscreen, mineral or not, reduces the SPF level and disrupts the formula's film-forming ability. Interference in the way the sunscreen forms a film on skin can affect its water resistance, how long it stays on skin overall, and whether it still protects evenly against UVA/UVB rays.
But you don't have to take my word on this – I'm not a cosmetic chemist or formulator or dermatologist. That's why almost as soon as I saw an Instagram post that recommended adding oil to mineral sunscreen, I contacted some key experts for their reaction. Here's what they said...
why you don't want to mix oil or serum or foundation with your sunscreen
Naomi Furgiuele, Senior Director of Global Beauty Face Care at Johnson & Johnson, makers of Neutrogena and Aveeno
Fun fact: Naomi has a background in chemical engineering.
"In a mineral sunscreen, the particles of zinc oxide or titanium dioxide work by reflecting light. In a non-mineral sunscreen, the sun filters form a film that helps prevent light from reaching the skin. Each sunscreen formulation is tested to determine the SPF rating – and each formulation is tested because the ability of the formula to protect the skin from sun exposure results from a combination of the formula, the sun filters and their levels in the formula, the way the consumer applies the sunscreen formula, and the way the sunscreen formula dries on the skin.
Any changes to the formula, including adding oil and/or tint could impact the way the sunscreen formula spreads and dries, and in turn impact the SPF protection provided by that formulation.
If you let the sunscreen layer dry, you can apply other things, like makeup, on top. However, pre-mixing products with sunscreen before applying to the skin is not a behaviour we would advise on.”
Stephen Baldwin, Senior Associate Director of Global Suncare Formulation Development at Bayer, maker of Coppertone
"You start messing with that sunscreen film and you start getting unpredictable consequences. In general, things that modify that film will modify the SPF unpredictably. The general recommendation for sunscreen application and makeup is to apply a sunscreen that you like, wait for it to dry, and apply your product on top."
Beautygeeks: But mineral sunscreen sits on the surface of the skin. Won't putting makeup over a mineral sunscreen therefore rub the sunscreen off?
Baldwin: In general if you have a good sunscreen with a good film former, once it sets up it's usually quite stable.
Beautygeeks: what if you apply a layer of sunscreen, let it set, then mix a drop of foundation with the sunscreen and put the new blend on top as a second application?
Baldwin: "That would be our recommendation. Apply a layer of SPF first. Once the sunscreen is laid down, it's usually pretty robust."
Marie-Hélène Lair, International Scientific Communication Director at Clarins
Fun facts: Marie-Hélène has a Doctorate in Pharmacy, was the scientific communication director at Chanel for more than 13 years, and for 10 years before that was the scientific communication director for Johnson & Johnson.
"Sunscreens are supposed to be applied alone because of the intensity of protection. When we test the strength of our SPF, it is always alone. It's a matter of the quantity of the product that you use. You need a golf-ball amount for your whole body. Then you'll have the intensity of protection offered on the label.
"If you use cream or oil with your product, you decrease the intensity of your protection.
"Sunscreen isn't only a matter of beauty, it's a matter of health. You don't play with that. You have to maximize your protection as we do in our labs.
"When it's a matter of mineral filters, they're powder. If you cut the homogeneity of the formula, you will have holes in the protection on your skin. In our labs we check the perfect homogeny of our product to make it not so white-ish and not so visible, but it's very complicated to make sure the consumer has a very homogeneous and protective formula. If you blend in whatever, you don't have a homogenous film over the skin, so all the UV rays can enter."
Dr. Julia Carroll, dermatologist and co-founder of Compass Dermatology in Toronto
"You're definitely affecting how the sunscreen sits on the skin, but the big thing is that once you dilute it, even a little, you've changed the SPF. And you don't know whether what you've diluted the sunscreen with de-activates the active ingredients – there are lots of things that can de-activate sunscreen or change its behaviour.
"Basically, if you add anything it's no longer a sunscreen – you can't guarantee its effectiveness if you dilute it with other things, particularly oil. You don't know the pH or stability anymore."
"Don't cocktail with SPF. You can cocktail with your other skincare; don't cocktail with your sunscreen."
Bill Baker, founder of Consonant Skincare, a popular all-natural Canadian line
"Strictly speaking, altering the formulation by adding either serum or additional lotion/cream could impact the SPF value. In order to know for sure, a 'Wavelength Test' would have to be conducted to determine the effective SPF value after the addition.
"The original idea of adding serum or lotion to aid with application (given the chalkiness that can occur from the ground, powdered minerals) was more of a 'beauty hack' than a clinical recommendation.
"We want to make sure we are not telling customers to put their skin at risk by lowering the effective SPF value. We recommend they make the skin comfortable first – i.e. blend HydrExtreme and Face Cream and apply – then follow with our mineral Sunscreen at full concentration."
what about pre-tinted mineral sunscreen?
Tinted mineral sunscreen solves the white-cast problem for many people, but for some of us, the tint is just a titch too dark. So what if we mix a drop of untinted mineral sunscreen with a bit of tinted mineral sunscreen?
Well, if the sunscreens are from different brands, we run the risk of disrupting the film it forms on the skin. However, La Roche-Posay makes an untinted mineral SPF 50 as well as a tinted version, as does SkinCeuticals. What if we mix same-SPF formulas from the same brand?
Chloe Smith, Natural Education and Scientific Communications Lead for SkinCeuticals doesn't foresee any harm in mixing Sheer Physical SPF 50 with Physical Fusion SPF 50. "The difference in the formula is the addition of tinted iron oxides in Physical Fusion," she says. But she also makes an important point: "Skinceuticals does not have any testing on the performance of our sunscreens when they are mixed together."
to add or not to add
Aaargh! Sunscreen just isn't easy, is it. It's an essential, like brushing our teeth, but way more complex. When it comes to altering a sunscreen to make it feel better on skin, is it enough that we're at least using it? Even if we can't know how much protection we're really getting, or whether we're getting uniform protection, is it enough to know that we've applied at least some more often than not? Can we take comfort from the adage that the best sunscreen is the one we willingly use daily, even if we haven't any idea whether the protection has been self-compromised?
This makes me wish I had my own SPF testing lab. What do you think? What do you do?