Mineral or chemical sunscreen: what the difference means for your skin

ROUTINE

Whichever filter you choose, the skincare underneath should be light and not contain a UV filter of its own, like The Duo – Serum & Face Cream.

How do mineral UV filters work?

Mineral UV filters consist of zinc oxide or titanium dioxide and absorb most UV radiation rather than reflecting it away from the skin. The image of a mirror is persistent, but it is not accurate. A series of measurements in the journal Photodermatology, Photoimmunology and Photomedicine shows that zinc oxide and titanium dioxide reflect only around 4 to 5 per cent of radiation across the entire UV range. By far the larger remainder is absorbed by the particles and converted into a very small amount of heat. At its core, then, the same thing happens as with an organic filter, only by a different physical route. For you, one thing follows above all: you need to apply a mineral product just as carefully and just as generously as any other sun product. A thin veil does not protect you, whichever filter it contains. Why UV radiation carries so much weight here is explained in our article on what actually slows down skin ageing.

How do chemical UV filters work?

Chemical UV filters are organic molecules that absorb UV radiation and release the energy again as heat. Well-known examples are avobenzone, octocrylene, homosalate, octisalate and newer filters such as tris-biphenyl triazine. They are soluble and can therefore be worked into light textures that remain practically invisible on the skin. That is their biggest practical advantage, because a sunscreen that feels pleasant is more likely to be used every day and in a sufficient amount. Some organic filters are less stable in light than others and are combined with partner filters in modern formulas so that the protection lasts while you wear it. That, too, is an argument for reapplying, not against this class of filter. Incidentally, chemical in this context only means that they are organic compounds. It says nothing about whether a product is well or poorly tolerated.

Mineral or chemical: a direct comparison

On most points, the comparison is a draw, because both types of filter achieve high sun protection factors and both are only permitted in Switzerland at tested maximum concentrations. The differences show up in how they feel to wear, how visible they are on the skin and how a formula is received by irritated skin. Mineral formulas get by with few filter substances and are therefore often the more straightforward choice for very reactive skin, especially if you already know that you react to many fragrances and auxiliary ingredients. Chemical formulas score on texture and everyday practicality, and are therefore more often used consistently. Which option suits you depends less on the class of filter than on how your skin is currently reacting and which product you actually reach for in the morning. The best sunscreen is the one you apply generously, not the one with the purer ingredient list on paper. We have explained separately what lies behind the term sensitive skin.

Why mineral sunscreen leaves a white cast

Mineral sunscreen leaves a white cast because, in visible light, zinc oxide and titanium dioxide do exactly what they barely do in the UV range: they reflect it. The same series of measurements that finds only 4 to 5 per cent reflection in the UV range measures up to 60 per cent in the long-wave and visible range. So the white sheen is not a formulation error but a direct consequence of the raw material. It can be reduced with smaller particles, with tinted versions containing iron oxides, and with formulas that distribute the filter better in the emulsion. With high proportions of zinc oxide, it will rarely disappear entirely. If the effect bothers you, there are two honest options: a tinted mineral version or a chemical product. What you should not do is apply less so that less is visible. That is precisely when you lose most of the protection.

Which UV filters are permitted in Switzerland?

In Switzerland, only the UV filters listed in Annex VI of the European Cosmetics Regulation 1223/2009 may be used. The Federal Food Safety and Veterinary Office (FSVO) refers directly to this list, with a few deviations set out in the Swiss Ordinance on Cosmetic Products (VKos). A substance that is not on it may not be used as a UV filter in a Swiss sun product, however natural it sounds. For zinc oxide, the maximum concentration is 25 per cent, and the same applies to titanium dioxide. Both are excluded from applications in which the lungs could be exposed, meaning sprays and aerosols. All filters are declared in the ingredient list, with nano forms additionally marked with the word nano in brackets. You can see exactly which substances our two products contain in the overview of all ingredients. Zinc is listed there at 1 per cent, but not as zinc oxide: what zinc PCA does in skincare has nothing to do with sun protection.

What this means for your routine if your skincare has no SPF

If your skincare has no sun protection factor, sunscreen goes on top as the last step, once the serum and cream have absorbed. The order is therefore serum, cream, sunscreen – in that sequence and with a few minutes in between, so that the protective film builds up evenly. The Duo, our serum and cream, deliberately contains no UV filter and therefore does not replace a sunscreen. In the evening the step falls away; in the morning it belongs in your routine on bright days. If you have to choose between skincare with a filter and two separate steps, two steps are the more reliable option, because you can dose the sunscreen independently of your skincare and reapply it during the day. How serum and cream work together day to day is explained in our article on whether you really need both, and you will find the exact amounts on the how to use page. For the Duo, that is 3 to 6 drops of serum and 3 to 6 pumps of cream, morning and evening.

One customer wrote to us that she had spotted zinc in the ingredient list and concluded that the cream provided some light sun protection. She wanted to know whether she could skip applying extra sunscreen on cloudy days. The answer was clear: no. Zinc in a skincare formula is not zinc oxide as a UV filter, and without a declared sun protection factor there is no sun protection, not even in small amounts. This mix-up happens often, because both terms contain the word zinc.

Frequently asked questions