As you probably have noticed, summer is in full swing in the northern hemisphere. For many, summer means vacation, barbecues, mosquitoes, and sunburns from UV rays. Many, many sunburns. Experts say that there are two good options for protecting yourself from the harmful effects of UV radiation: 1) cover yourself using protective clothing, hats, sunglasses, and avoid being outside when the sun is the strongest; and 2) apply sunscreen regularly. These seemingly straightforward defense techniques can protect us from both sunburns and, more importantly, the increased risks of skin cancers that often come alongside them. Skin cancer is the most common type of cancer worldwide (NHS website, 2020) and UV radiation has been linked to both nonmelanoma skin cancers (NMSC) and a large percentage of melanomas; and you decrease your likelihood of getting these cancers significantly by taking appropriate protective measures. Meaning, it is super important to protect yourself from too much UV radiation. One of the most effective and affordable ways to do so is to apply sunscreen. We all know what sunscreens are, that they have different sun protection factors (SPF), and that come in different shapes and forms. But how do they actually work? And are all sunscreens equally good for humans and for the environment? Spoiler alert, they are not.
This week we are going to discuss why some sunscreens aren’t as good as others and how you can pick the best sunblock for your next vacation.
How does sunscreen work?
In order to understand why not all sunscreens are created equal, it’s important to learn how sunscreen is designed to protect you from the ultraviolet radiation (UV rays) produced by the sun. Sunscreen uses two approaches to keep you safe - physical and chemical. Physical protection is provided by zinc oxide and titanium dioxide which basically work like a mirror to reflect the UV rays off of your skin - preventing them from being absorbed by your body. Then the chemical mixture in your sunscreen reacts with the UV rays from the sun, and releases the absorbed energy from the sun as heat (Isguven, 2012).
The sun protection factor (SPF) rating on your sunscreen is an indicator of how much longer it would take for the average person to get a sunburn while wearing the sunscreen. For example, with SPF 15 applied exactly as directed, it would take someone 15 times longer to burn than if they weren’t wearing any sunscreen. An SPF 15 allows approximately 7% of UVB rays to hit your skin. An SPF 30 reduces this number to about 3%, thus being more than twice as effective as an SPF 15. Does this mean that we should use the highest SPF we can find and go to the beach without worrying too much about burns and cancer? Well, not really. In the ideal conditions, a broad spectrum sunscreen with a high SPF does offer more protection against UV rays. However, people using extremely high SPF sunscreens tend to lower their guard against UV radiation thinking that this high SPF is sufficient. They neglect other lines of defense (hats, protective clothing, seeking shade), they tend to stay in the sun longer, and they may not reapply sunscreen as often as required. So counterintuitively, they may get more UV damage by using a high SPF because of the false sense of full protection.
Why are some sunscreens better than others?
The good news is that researchers agree that the physical protection ingredients in sunscreen - zinc oxide and titanium dioxide are safe and effective (EWG’s Guide to Sunscreens, n.d.). The bad news is that the chemical ingredients in some sunscreens haven’t passed the safety and efficacy tests in a consistent manner. Further detailed studies are required to demonstrate complete safety -or lack of- of some of the chemical components. What we currently know is that sunscreens contain at least 12 common ingredients that may not provide any significant protection from harmful UV rays to the consumers (data from the Environmental Working Group).
One of the most concerning ingredients from this list is oxybenzone (reviewed in DiNardo et al 2021). This ingredient is worrisome for a number of reasons. First of all, data suggest that this chemical can be absorbed in large quantities through the skin, and if this absorption happens over a long period of time it could disrupt the endocrine system of the wearer. This conclusion was reached because oxybenzone has been detected in human breast milk, amniotic fluid, and urine - all telltale signs that a chemical can be absorbed through the skin (Brown, 2019). This is a problem because the endocrine system is a network of glands in the body responsible for regulating metabolism, reproductive hormones, sensory perception, sexual development, and growth (Hormone 2019). Various studies in animal models have identified severe negative impacts of oxybenzone in the development of breast tissue in mice and even sex change in fish embryos (Fivenson et al 2020). Although results from animal studies don’t always translate directly to humans, all of this taken together illustrates that the impact of oxybenzone in sunscreen warrants further investigation. In addition to potential negative impacts of this ingredient in people and model lab organisms, oxybenzone has been confirmed to have negative impacts on the environment. In fact, several locations have banned sunscreens that contain oxybenzone because of its connection to coral bleaching (Danovaro et al 2008; Brown, 2019). For example, the state of Hawaii is on its way to ban distribution of certain sunscreens (unless with a prescription) to reduce the unprecedented levels of coral bleaching across all of the state’s islands. A recent scientific review highlighted the fact that oxybenzone and other related chemical UV filtering ingredients have been detected in nearly all water sources around the globe. This ingredient is kind of a double whammy - it threatens fragile ecosystems AND it is difficult to remove in wastewater treatment plants (Schneider et al 2019). This means that if we want to remove this poorly studied ingredient from our water systems, we will need to implement new, potentially costly techniques.
It is important to note that claims concerning human health and oxybenzone are still being investigated by the United State’s FDA (federal drug agency), and research into the direct impacts of long term exposure of oxybenzone in humans is still limited. But that doesn’t make the current data less worrisome.
Take home message - How do I pick the best sunscreen? We don’t know for sure if oxybenzone is safe over the long term for humans, but we are confident that it is terrible for the environment. We also have data demonstrating that overexposure to UV radiation highly increases the risk of developing skin cancer. So what should we do? Several organizations put together lists of sunscreens that are good alternatives to the ones containing questionable ingredients like oxybenzone. The Environmental Working Group and New York Time’s Wirecutter are among the organizations providing such lists. So a sensible thing to do would be to familiarize yourself with such lists before clicking that buy button in your online shopping cart.
The last question that we are going to touch on in this post is whether sunscreens cause changes in our skin’s microbiome. How do millions of microorganisms that live on our skin feel about a chemical cocktail designed to protect us against skin burns and cancer? The short answer is the same that you have been hearing a lot lately, in relation to science and the COVID-19 pandemic - we don’t know. It is possible and even likely that many chemical components of the average sunscreen will change the skin environment, thus challenging bacteria to new conditions. The good news is that currently there are no studies demonstrating a long term negative effect of sunscreen on our skin’s microbiome. The physical structure of the skin probably protects its microbiome against sunscreen similarly to how it protects it against antimicrobial agents. After we wash our hands or apply antimicrobial products, we remove many microbes from the surface of our skin, only for it to be repopulated within minutes by the same microbes that were hiding deeper in the skin. This is why many dermatological associations continue to recommend the use of sunscreen before going out. Needless to say, that further research on this subject is highly anticipated.
References:
Isguven, S. (2012, June 9). How Does Sunscreen Protect You? – Yale Scientific Magazine. Yale Scientific Magazine. https://www.yalescientific.org/2012/05/how-does-sunscreen-protect-you/
EWG’s Guide to Sunscreens. (n.d.). EWG’s Guide to Safer Sunscreens. Environmental Working Group. Retrieved July 6, 2021, from https://www.ewg.org/sunscreen/report/executive-summary/
DiNardo JC, Downs CA (2021) Failure to Protect: Do Sunscreens Prevent Skin Cancer in Humans? Toxicol Open Access 7: 1000157.
Brown, J. (2019, July 23). Sunscreen: What science says about ingredient safety. BBC Future. https://www.bbc.com/future/article/20190722-sunscreen-safe-or-toxic
Hormone. (2019, May 24). The Endocrine System. Hormone Health Network. https://www.hormone.org/what-is-endocrinology/the-endocrine-system
Fivenson D, Sabzevari N, Qiblawi S, Blitz J, Norton BB, Norton SA. Sunscreens: UV filters to protect us: Part 2-Increasing awareness of UV filters and their potential toxicities to us and our environment. Int J Womens Dermatol. 2020 Sep 9;7(1):45-69. doi: 10.1016/j.ijwd.2020.08.008. PMID: 33537395; PMCID: PMC7838327.
Danovaro, R., Bongiorni, L., Corinaldesi, C., Giovannelli, D., Damiani, E., Astolfi, P., Greci, L., & Pusceddu, A. (2008). Sunscreens cause coral bleaching by promoting viral infections. Environmental health perspectives, 116(4), 441–447. https://doi.org/10.1289/ehp.10966
Schneider SL, Lim HW. Review of environmental effects of oxybenzone and other sunscreen active ingredients. J Am Acad Dermatol. 2019 Jan;80(1):266-271. doi: 10.1016/j.jaad.2018.06.033. Epub 2018 Nov 14. PMID: 29981751.
HS website. (2020, September 4). Skin cancer (non-melanoma). Nhs.Uk. https://www.nhs.uk/conditions/non-melanoma-skin-cancer/
https://www.skincancer.org/blog/ask-the-expert-does-a-high-spf-protect-my-skin-better/
https://thesecretlifeofskin.com/2020/07/01/uv-sun-and-the-skin-microbiome/
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