Are sunscreens safe

UV filters can get into the blood : How dangerous is sunscreen really?

Whether cream, lotion or spray: Consistent lubrication protects against sunburn, skin cancer and skin aging. The UV light filtering substances contained in sunscreens are responsible. And it is precisely these that cause uncertainty. For one thing, there are a multitude of ingredients with complicated names that even doctors and pharmacists find difficult to keep track of. On the other hand, there are discussions as to whether the means could possibly have dangerous side effects. But are they so serious that it would be advisable not to use lotion?

Some filter substances can be detected in the blood just one day after applying the cream

There are two groups of sun protection filters: Organic filters, often incorrectly referred to as “chemical”, absorb the UV rays and convert them into heat and harmless fluorescent light. Inorganic (or mineral) filters are primarily understood to mean zinc oxide and titanium dioxide. They form a barrier on the skin where they scatter, reflect and absorb UV light. In the past, such inorganic filters made the skin white, today they are often incorporated into the creams in the form of nanoparticles, so that this "whitening effect" does not occur. The label “nano” can then be found on the packaging after the filter name. However, because no substance alone covers the entire spectrum of UV radiation, common sunscreens usually contain various filters in order to provide as comprehensive protection as possible.

Organic filters hit the headlines last spring. The US Food and Drug Administration (FDA) had investigated whether filter substances contained in commercially available sunscreens could get into the blood. To do this, the 24 test participants had to apply the recommended amount of two milligrams per square centimeter to 75 percent of their body surface four times a day for four days.

The subsequent blood analyzes showed that all four organic filters examined (avobenzone, oxybenzone, octocrylene and ecamsul) were detectable in the blood from day one. The results cannot be used to infer a harmful effect, according to an accompanying commentary on the study in the journal “Jama”. But the authors call for further investigation for the United States, where sunscreens are classified as over-the-counter drugs.

In feeding experiments, three filter fabrics made the uterus of rats grow

In the EU, sunscreens do not trade as medicines, but as cosmetics. Only approved UV filters may be used. The Scientific Committee for Consumer Safety (SCCS) of the EU Commission is responsible for the examination, an expert committee to which Gisela Degen belonged for ten years. Until her retirement in 2016, the professor of toxicology headed the Chemical Risks Working Group at the Leibniz Institute for Labor Research at TU Dortmund University.

“It has been known for a long time that organic filters are absorbed through the skin,” says Degen. The filter substances are dissolved in the cream and can penetrate from the surface of the skin into the deeper layers of the skin. As these are supplied with blood, the filter materials are absorbed into the bloodstream to varying degrees. “This is the case to a very small extent with most organic filters,” says Degen. They would later be filtered from the blood by the kidneys and excreted in the urine. The only question is what is happening in the body in the meantime.

In the discussion about organic filters, the main question is whether the substances can upset the hormonal balance. The focus is usually on an estrogen-like activity, i.e. an effect similar to that of the female sex hormone estradiol, which in humans is mainly formed in the ovaries. Scientists test such activity in studies with cell cultures, among other things. To do this, they bring UV filters together with those cell types that have docking sites for certain hormones.

If these receptors are stimulated by the test substance, this is a sign that it has a hormone-like effect. “You can measure whether the cells are dividing faster under these circumstances,” says Degen. This was the case in studies with some organic filters. But that alone is by no means proof of a hormone-like effect in humans. According to Degen, the main reason why such experiments cannot simply be transferred to the situation in the body is that not everything that is smeared on the skin also reaches the organism. The percentage that crosses the skin barrier is determined, for example, in experiments on pig or human skin. For many organic filters, this proportion is less than one percent, says Degen.

It is true that in the European Union it has been completely forbidden to test the ingredients of cosmetics in animal experiments since 2013. Most of the filters were approved beforehand, however, and their safety was therefore often tested on animals, such as rats that were given UV filter substances in different doses every day in order to observe possible changes in hormone levels or in their reproductive capacity. Researchers also used rodents to investigate whether UV filters can stimulate the uterus to grow.

If this is the case, it speaks in principle for a hormone-like effect. In fact, the uterus grew from rats whose food researchers at the University of Zurich had mixed with three different filter materials in 2001. However, it is a different matter whether such a substance is ingested with food or smeared on the skin, says Degen, because this results in very different concentrations in the body. Therefore, the results could not easily be transferred directly to humans.

Transferability to humans uncertain

The EU approval procedure for cosmetics does not provide for tests on humans, especially since, according to Degen, it would be difficult to measure a hormonal influence anyway because the human hormone level naturally varies. In order to evaluate the safety of organic UV filters in humans, the SCCS experts use the content in the total sunscreen (usually four to ten percent), the amount applied and the rate of absorption through the skin. This is how they determine a possible internal dose in humans.

This must be at least a hundred times lower than one that no longer showed any undesirable effects in animal experiments. The toxicologist Degen says that in the evaluations of the SCCS there is no evidence of hormone-like or other harmful effects of the organic filters approved in the EU in humans. Therefore, she sees no reason to classify this type of sun protection filter as a medication in this country: "Anyone who makes this requirement would first have to prove that the current approval process is not suitable."

The pharmacologist Christian Surber from the dermatological university clinics in Basel and Zurich also considers the EU approval process to be safe. Nevertheless, he recommends pregnant women and breastfeeding mothers, as a precaution, to use sunscreen products that only contain mineral filters for themselves and their children. Because children in particular have a large skin surface in relation to their body mass and therefore absorb a larger amount of the organic filter substances based on their weight.

For Surber an argument in favor of the mineral alternatives: "Zinc oxide and titanium dioxide do not go through the skin" - especially not if the substances are in the classic "micronized" form, which then leaves the white layer on the skin when applied. According to the Swiss, the substances do not penetrate the skin even if they are incorporated into sun protection products as nanoparticles. This is mainly due to the fact that the molecules of the mineral filters, despite their nano designation, are ten to a hundred times larger than those of more modern organic filter materials. This makes it impossible for them to wander into deeper layers through the tiny gaps between the skin cells.

The all-clear from the Federal Institute for Risk Assessment

The Federal Institute for Risk Assessment also classifies the application of nanoparticles to intact and sunburn-damaged skin as harmless. The authority only advises against sprays with nanoparticles, as investigations are still being carried out at the moment to determine what effects the particles can have if they get into the airways. The pharmacologist Christian Surber considers them unsuitable anyway. “On the one hand, studies show that most people do not apply enough of the solution.” A large part of the sunscreen is lost to the environment when it is sprayed. And if you spray the product into the cupped hand and then rub it in, you are using it correctly, but you don't need to buy expensive sprays either.

The filters included in the products are usually listed on the back of the sunscreens. If you want to make sure that you buy a product with only mineral filters, but lose your bearings in the tangle of chemical names, you can ask in the drugstore or pharmacy.

The circular UVA logo should be visible on the packaging so that a sun cream not only protects against the UVB radiation that causes sunburn, but also against the UVA radiation that can age the skin. Some manufacturers would simulate this, for example in the form of a yellow sun with an "A" or "UVA" in the middle. In that case, Surber warns, protection is not guaranteed.

He is similarly skeptical about indications such as “coral-friendly” or “reef-friendly” on sun creams that do without octinoxate and oxybenzone. These filter materials are suspected of promoting coral bleaching or damaging the genetic make-up of fish and corals. However, says Surber, these findings came from tests in aquariums and it is by no means clear whether the UV filters have an impact on corals and marine life under real conditions. In Hawaii, however, such sunscreens will be banned from 2021.

Conclusion:There is no reason not to put on sunscreen - at least protection factor 30, at the sea and in the mountains 50, and ideally in addition to protective clothing and the right behavior (such as looking for shade between 11 a.m. and 3 p.m.), advises Surber. Because although there may never be a guarantee that UV filters will not trigger any effects in the body: It is certain that they protect the skin from sunburn and skin cancer.

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