Sunscreens that work well on their own may not be as effective when combined. New research shows that they can create toxic byproducts in certain combinations.
Zinc oxide is being promoted as a safer, chemical-free alternative to sunscreens. However, this depends on the product it's paired with.
Researchers say that the inorganic sunblock can be used under or over other organic sunscreens. This means that the Sun's ultraviolet rays aren’t as blocked as the products on their own.
Researchers discovered that the mixture would cause the organic UV-filters to lose their effectiveness, which could lead to potentially harmful products.
The potential toxicity of sunscreens in the current study was tested only on zebrafish and not humans. However, these creatures are genetically very close to us. They are also representative of other sea fish, which could be affected by the sunscreen that we use.
Researchers say that we shouldn't layer these products over each other until we learn more. This is not only for our health, but also for the health of the environment.
However, this doesn't mean that sunscreen should be stopped altogether. We can be sure that too many people have died from skin cancers due to high sun exposure.
Richard Blackburn, University of Leeds materials scientist, says that sunscreen should still be used. However, he suggests that consumers avoid mixing sunscreen and zinc oxide. This could be done either intentionally or by accidently mixing sunscreen with other products, such as SPF makeup.
Although many other studies have demonstrated that sunscreens react quickly to UV exposure, few researchers have investigated whether the reaction produces toxic byproducts.
Sunscreen chemicals have been approved only as an individual chemical and not as a mixture of chemicals.
Researchers tested five sunscreens that have a sun protection factor greater than 15 to better understand the reactions of the sunscreen chemicals in Europe and the United States.
The team tested the safety and effectiveness of the chemical formulas, when they were combined with zinc oxide and exposed to sunlight for two hours.
These results show that even a small amount of zinc oxide can reduce the protection of your skin from ultraviolet A rays. This is because it is often mixed with non-mineral sunblocks.
A mixture of non-mineral sunblocks only lost 15.8 percent of its UVA protection without any zinc oxide.
Although the Sunblocks based on small molecules don't degrade much, the study didn't test commercial sunblocks directly.
Researchers warn that sunblock shelf chemicals and preservatives could alter the results. This should be investigated further.
The authors recommend that you avoid mixing zinc oxide and other sunscreens until then. Even though makeup may contain SPF, this could affect the product's effectiveness and safety.
Researchers noticed that zebrafish embryos were more toxically affected by zinc oxide when they were exposed to different chemical and zinc oxide combinations for five days in sunlight.
These products didn't cause death, but the zebrafish did show some morphological defects.
The authors conclude that "these results suggest that zinc oxide particles could increase sunscreen toxicity, in ways not currently recognised".
They add that they fear that products with unintended consequences or chemical substitutions will be created by the increasing use of UV-filters, in particular metal oxide particles.
There aren't many alternatives to zinc oxide that have been approved by the US government. They can still filter the Sun the same way. However, in Europe, other inorganic substances are approved to be used as sun filters. These ingredients don't seem as toxic and break down as easily as zinc oxide.
The solutions were mixed with dimethyl sulfoxide, an agent that makes them more water-soluble to test for potential toxicities. Although sunscreens do not contain this chemical, it is worth continuing to study the potential dangers to wildlife and humans from any chemical that could have potentially dangerous consequences.
We have been warned about dangerous sunscreens before. For example, a UV-filtering chemical compound found in 3500 sunscreen brands has been shown to inhibit the growth of corals and make them more vulnerable to bleaching events over years. Yet, these ingredients are still used frequently.
People are becoming more concerned about sunscreen chemicals in recent years. However, research and regulation of these ingredients is still a long way off.
It's not only sunscreen. Many cosmetic products we use every day are not properly safety tested. Some cosmetic products have been identified as potentially toxic or carcinogenic in Europe, but remain commercially available in the USA.
It is difficult to fill this vast knowledge gap. This is made more difficult by the possibility that chemicals could become toxic if they are altered in any way or mixed with other products.
The sunblock paper authors conclude that "Overall," they say, "more research is needed to study sunscreen formula phototoxicity and photostability in order to guide design and mass-production of safe and effective formulations."
The study was published by Photochemical & Photobiological Sciences.
