Excessive exposure of the skin to sunlight can lead to many negative effects, such as sunburn, photoaging, and skin cancer development.  One way to prevent the damages caused by sun exposure is to use sunscreens. Sunscreens block the penetration of UV rays through the epidermis by absorbing and/or reflecting them.  Accordingly to the European Commission, the adequate amount of sunscreen to reach the Sun Protection Factor (SPF) indicated in the label is 2 mg/cm² which equals 6 teaspoons of lotion (approx. 36 grams) for the body of one average adult person.  Applying a smaller quantity means a reduced protection.
Sun protection in sunscreens can be provided by chemical or physical UV filters. But, what is the difference between them?
Chemical sunscreens are absorbed into the skin and absorbs the UV light converting it into heat. The active ingredients in chemical sunscreens include avobenzone, octinoxate, and oxybenzone.
Physical sunblocks act by blocking and reflecting the sun’s rays. The minerals titanium dioxide and zinc oxide are the main active ingredients in physical blocks. 
The possible harmful effects of chemical filters, such as those containing oxybenzone, to the environment and to human health are currently being debated by the scientific community. Studies have identified UV filters containing oxybenzone, octocrylene, octinoxate, and/or ethylhexyl salicylate in almost all water sources around the world and have commented that these chemicals are not easily removed by common wastewater treatment plant techniques.  Some studies have also shown the presence of oxybenzone in the urine of human volunteers four days after application on the skin. This suggests that oxybenzone can pass into the circulatory system and may have potential effects on internal organs. 
But what does this mean?
There is not clear evidence or sufficient studies about the toxicity of those chemical filters. According to the FDA, oxybenzone has been used for over 40 years in sunscreens and also in other cosmetic products, such as fragrances, make up, nail polish and others. In fact, after 40 years of use, there is no awareness of any published study that demonstrates acute toxic effects in humans with systemic absorption of oxybenzone.  However, in 2019, the FDA concluded that 12 active ingredients commonly found in sunscreens, including oxybenzone, need additional safety data. 
While the industry can say that there is no correlation between cause and consequence for those compounds, it is worth noting that we cannot be 100% sure that they are not harmful at some level. There are always two sides to the coin. Hence, we should always look for sources and studies that don’t contain bias.
Even though we still don’t have all the answers, we can make more conscious decisions about the cosmetic products we use and be aware of their possible impacts on us and on the environment.
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Photoprotection: facts and controversies
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 Wang SQ, Burnett ME, Lim HW. Safety of Oxybenzone: Putting Numbers Into Perspective. Arch Dermatol. 2011;147(7):865–866. doi:10.1001/archdermatol.2011.173
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