Sunscreen. A necessary evil?
Every third cancer diagnosis in Germany is a skin cancer diagnosis. This means 275.000 cases per year, in Germany only. Even more dramatic numbers are reported from Australia, where 6 out of 10 inhabitants are diagnosed with skin cancer within their life (1). Risk factors are pale complexion with freckles and previous skin cancer diagnoses within the family. But above all, damage to the skin during the early youth and childhood is a critical factor. Therefore, it is crucial to avoid long exposure to direct sunlight, and to always wear sunscreen, textile protection, and sunglasses. MyMicrobiome scrutinized sixteen common sunscreens regarding their microbiome-friendliness. Read on for the (anonymized) details.
UVA and UVB radiation
The most aggressive part of the sunlight is in the ultraviolet spectrum, or UV radiation. It is separated in UVA and UVB (also UVC which shall not be analysed here).
UVA radiation causes hyper pigmentation, loosened skin, and wrinkles, so premature skin ageing. It can intrude into the tissue so deeply that it can cause damage to the dermis, meaning the collagen and elastin fibre layer are degraded, free radicals are released, and irreversible damage is caused. The worst case is the production of melanoma, the most dangerous form of skin cancer. 100% of the sun’s UVA radiation reaches the earth’s surface throughout the entire year in the same intensity, and it also pervades window glass. The European Commission recommends 1/3 of the sunscreen’s filters to be exclusively against UVA radiation (17). For this reason, the COLIPA (European Cosmetic and Perfumery Association) created a seal showing the letters UVA in a circle as standard on European sunscreen.
UVB radiation reaches down to the dermis where it triggers the production of melanin that makes a tanned complexion. It is richer in energy and spreads in the biologic tissue, fostering sunburn and in the worst-case causes cancer by long-term damage to the DNA. The only positive side of UVB radiation is the body’s own production of vitamin D, which is subject to chances depending on the intensity of the radiation throughout the year.
Especially children’s skin is so thin that the stem cells below can be damaged by UV radiation and cell mutations can occur (2). At the same time, sensitive children’s skin (and adult’s skin, too) should be treated with particular care without any additional harmful substances. A product that is applied daily over months should be selected very thoughtfully.
But in the end, every sunscreen is better that a sunburn. A sun protection factor of 30 with a protective effect of 95% is sufficient. Products with higher protection factor such as SPF 50 have an additional 3% of protective effect (so, 98% in total), but come with disproportionate more stress for the skin by ingredients.
Filter in sunscreens
Skin cancer is associated with UV radiation. An interesting fact is that the typical skin bacterium Staphylococcus epidermidis produces 6-N-hydroxyaminopurine (6-HAP), which can inhibit skin cancer cells (4).
Sunscreens work with filters by reflection, dispersion, or absorption of harmful UVA and UVB radiation. There are two different approaches, the organic-chemical and the mineral-physical (17).
Mineral filters reflect the sunlight and keep it from entering deep skin layers. The most common mineral filters are titanium dioxide and zinc oxide. They are generally a bit less convenient to apply and leave a “whitewash” on skin and textiles. Manufacturers try to cope that unpleasant characteristic by downsizing microparticles to nano particles with a benchmark value of 330 nm. The application is much more convenient, but is has not yet been finally clarified whether nano particles can diffuse the skin barrier and enter the body. Sunscreen with nano particles should not be used for babies and infants for that reason and also adults with irritated or injured skin are advised to better not use products with nano particles.
Chemical filters used to work on octocrylene basis and other absorbers that are today at least controversially discussed. In Germany, octocrylene was the most common filter. Meanwhile, there are a number of modern, organic-chemical UV filters for the entire UVA and UVB spectrum that are considered safe for the human organism. They do not penetrate the skin and do not cause allergic or phototoxic reactions, and also do not have an impact on the hormone system. It is advisable to use products that work with a synergistic combination of filters to cover the entire spectrum of UVA and UVB radiation.
It is also worth mentioning that in the US, some harmless filters are not or not yet accredited, because they are regulated as prescription-free medication by the FDA. On the contrary, the European regulatory boards assess these filters as cosmetics (17).
Octocrylene, Oxybenzones und Octinoxates
Octocrylene is one of 27 officially approved UV filters in the EU. There are indicators, however, that the substance is hormone active. This means that in case of a critically high entering of octocrylene the reproductive organs might be impaired, and fertility reduced (5). Especially with children, between the application of the substances and the possible problems with the reproductive organs can be decades. Urine probes confirmed octocrylene enters the body over the skin barrier and showed positive results even several days after the application (6). An info article by BBC health summarizes that also pregnant and nursing mothers should refrain from using the above-named O-filters (7). Hormone-active substances could transfer to the foetus or over the breastmilk to the baby and cause damage that might manifest after years. Of course, it is close to impossible to draw causal links over such a time span and it also practically impossible to find scientific prove in studies. So, those substances are up to date not forbidden, but many cosmetic producers reacted on critical publications and amended their formulations for sunscreens.
Another side-effect is that the substance is not stable which limits the expiration date to one summer season. After that the risk for allergies is ever higher than it is anyway (8). Over time, octocrylene transforms into the toxic benzophenone (9 and 10), which is under suspicion to cause cancer and effect fertility. Not only the consumer advice centre NRW is recommending refraining from that filter (11). Plus, octocrylene accumulates ubiquitous in flora and fauna when washed off the skin in water. It considerably contributes to coral death. The same goes for the other “O’s”: Oxybenzone and Octinoxate. For that reason, those filters are banned on Hawaii since 2021 and on Palau from 2023 onwards (12).
Titanium dioxide and zinc dioxide
As mentioned above, the mineral filters titanium dioxide (TiO2) and zinc oxide (ZnO) are often downsized to nano particles and could enter the body. It should also be mentioned that titanium dioxide is suspected of being genotoxic and carcinogenic after inhalation. The use is currently discussed more and more controversial in this regard, but at least, this suspicion could not be confirmed explicitly until now (13).
Also zinc oxide is used as a mineral alternative. But as zinc is widely bactericide, fungicide, and also toxic against protozoa (15), it is definitely not recommendable regarding microbiome-friendliness (despite it is often used in medicine for that characteristics). Anyway, zinc generates DNA damaging free radicals when exposed to sunlight – a rather inconvenient fact for a sunscreen ingredient. To keep the zinc oxide from reacting, many producers coat the particles. The coating is usually done on oil-base, which brings up the next problem. When the particles are on nano-size – and very often they are, for reasons mentioned above – they carry yet another substance into our bodies: a sheer unmanageable goal to find out what that substance is and what effects it might bring along.
Our test run
The products were (with one exception) selected on requirements for modern UV filters that are currently considered harmless. 14 products had a sun protection factor (SPF) of 30 and two more SPF 50 and 20. The goal was to clarify if there are any modern filters that would not affect the skin microbiome. The test run does not claim to be exhaustive, and the results are therefore published without naming the tested brands. The test was financed and executed by MyMicrobiome AG and does not underly any third-party interests.
No relevance was awarded to fragrances, denatured alcohol, microplastic, nano particles, parabens, silicones, mineral oil derivates, as well as the use of additional antioxidants. Antioxidants, however, would have meant a positive effect on the results.
Ahead of the test runs, the team defined four microbes that are typical for the facial skin microbiome (bacteria and yeasts). In vitro and under controlled conditions, the effect of the sunscreen on these microbes was tested, the results were documented and evaluated statistically.
The winner of our tests was a sunscreen formulated of six chemical filters and the mineral filter TiO2 (nano). From the ranking of the other products, one cannot conclude explicitly that the used filters would affect the skin microbiome negatively.
Products with zinc oxide or in combination with titanium dioxide scored last rsp. third-last. The sunscreen formulated with ethylhexyl methoxycinnamate (generally rated as critical) scored second-last. The sunscreens ranked last, seconds-last and third-last showed a strong reduction or complete cessation of microbial growth or several genera.
Sunscreens with ZnO are antibacterial and fungicidal and therefore not Microbiome-friendly. TiO2 does not appear to have an affect on the skin microbiome as it was in formulations of sunscreens that achieved good or very good results.
Those UV filters that are included in formulations that do not interfere with the growth of bacteria and yeasts in the tests are sufficiently suitable for use in microbiome-friendly products, but this is not a necessary condition.
Conclusively, the total formulation must be taken into account, as the active ingredients can have a reciprocal effect with the other ingredients. Likewise, the formulation can include antibacterial ingredients, preservatives, scents of aetheric oils etc that might have a negative impact on the microbiome.
Infobox on filters used
The tested sunscreens used combinations of various UV filters. 3 to 6 chemical filters, 5x in combination with the physical filter TiO2.
Used chemical UV filters
|INCI name / chem name||Trading name||Filter spectrum|
|Diethylamino Hydroxybenzyl Hexyl Benzoate||Uvinol A Plus||UVA|
|Diethylhexyl Butamido Triazone||Iscotrizinol||UVA + UVB|
|Bis-EthylhexyloxyPhenol Methoxyphenyl Triazine||Tinosorb S||UVA + UVB|
|Ethylhexyl TriazoneTriazine||Ethylhexyl Triazone Uvinol T150||UVB|
|Phenylbenzimidazole Sulfonic Acid||Enzulisol||UVB|
|Tris-Biphenyl Triazine (Nano)||Tinosorb A2B||UVA II + UVB|
Used physical UV filters
|INCI name||Trading name||Filter spectrum|
|TiO2||Titandioxid||UVA + UVB (nicht ganzes Spektrum)|
|TiO2 (Nano)||Titandioxid (Nano)||UVA + UVB|
Sources / References:
(1) Deutsches Ärzteblatt. Australien: Fälle von Hautkrebs nehmen zu. (1997) https://www.aerzteblatt.de/archiv/8593/Australien-Faelle-von-Hautkrebs-nehmen-zu
(2) Deutsche Krebshilfe. Hautkrebs. (2021) https://www.krebshilfe.de/informieren/ueber-krebs/krebsarten/hautkrebs/
(3) Cancer Council. Slip, Slop, Slap, Seek, Slide. (2021) https://www.cancer.org.au/cancer-information/causes-and-prevention/sun-safety/campaigns-and-events/slip-slop-slap-seek-slide
(4) Nakatsuji T, Chen T H et.al, A commensal strain of Staphylococcus epidermidis protects against skin neoplasia, Science Advances (2018), https://advances.sciencemag.org/content/4/2/eaao4502
(5) Gomes E, Pillon A, Estrogenic activity of cosmetic components in reporter cell lines: parabens, UV screens, and musks, Nat Libr of Med (2005), https://pubmed.ncbi.nlm.nih.gov/15799449/
(6) Bury D, Koch M H, et. al. Expositions-Biomarker für die UV-Filter Octocrylen und 2-Ethylhexylsalicylat, ASU Arbeitsmed (2019), https://www.asu-arbeitsmedizin.com/wissenschaft/expositions-biomarker-fuer-die-uv-filter-octocrylen-und-2-ethylhexylsalicylat
(7) Brown J, Suncreen: What science says about ingredient safety, BBC health (2019), https://www.bbc.com/future/article/20190722-sunscreen-safe-or-toxic
(8) deGroot A C, Roberts D W, Contact and photocontact allergy to octocrylene: a review, Wiley Online (2014), https://onlinelibrary.wiley.com/doi/full/10.1111/cod.12205
(9) Down C A, DiNardo J C et al. Benzophenone Accumulates over Time from the Degradation of Octocrylene in Commercial Sunscreen Products, Chem. Res. Toxicol. (2021), https://pubs.acs.org/doi/10.1021/acs.chemrestox.0c00461
(10) IARC Monographs, Benzophenone (2018), https://monographs.iarc.who.int/wp-content/uploads/2018/06/mono101-007.pdf
(11) Verbraucherzentrale NRW, Krebserregende Stoffe in alter Sonnencreme? (2021) https://www.verbraucherzentrale.nrw/schadstoffe/kosmetik/projekt-schadstoffberatung/schadstoffberatung-kosmetik/krebserregender-stoff-in-alter-sonnencreme-58458
(12) National Geographic, Nachhaltig reisen: Sonnencreme ohne Alles (2020) https://www.nationalgeographic.de/umwelt/2020/06/nachhaltig-reisen-sonnencreme-ohne-alles
(13) Deutsche Apotheker Zeitung, Wie gefährlich ist orales Titandioxid? (2021) https://www.deutsche-apotheker-zeitung.de/news/artikel/2021/05/12/wie-gefaehrlich-ist-orales-titandioxid
(14) Beyer & Söhne, Nanopartikel in der Sonnencreme – sind sie gefährlich? (2021) https://www.beyer-soehne.de/nanopartikel-in-der-sonnencreme/
(15) Das PTA Magazin, Zinkoxid lässt Keimen keine Chance (2019) https://www.das-pta-magazin.de/zinkoxid-laesst-keimen-keine-chance-2447293.html
(16) Gomes E, Pillon A, Estrogenic activity of cosmetic components in reporter cell lines: parabens, UV screens, and musks, Nat Libr of Med (2005), https://pubmed.ncbi.nlm.nih.gov/15799449/