With the summer around the corner, I thought it would be a good idea to look at what sunscreens actually are and do. We are supposed to apply it over our whole body and multiple times a day, so the ingredients in sunscreen should not be irritating or cause skin allergies.
First let's look at the two kinds of sun blockers. The first one is the physical kind, like zinc and titanium dioxide, and the second is the chemical kind, like oxybenzone, avobenzone, octisalate, octocrylene, homosalate and octinoxate. The former blocks or scatters the sun’s rays (literally), and the latter causes a chemical reaction and absorb the sun’s UVA and UVB rays. The problem with the first kind, mineral sunscreens, is that in the form it is used in sunscreen, the nanoparticle form (ultra-fine specs of material used in sunscreens to block or scatter the sun’s rays), the nanoparticles may be small enough to enter your bloodstream through the skin. Those concerns have grown louder since a recent study found that mice injected with titanium dioxide nanoparticles developed inflammation, a marker of cell distress that has been linked to, amongst others, aging and cancer. Sunscreens that contain titanium dioxide and zinc in non-nano form don't share these problems. The problem with the second kind is that animal studies have shown that some of these chemicals could cause damage to a person’s endocrine system. But many of the animal studies researching sunscreens involve injecting or inhaling the chemicals, not rubbing them on your skin. As of today, there is not much hard data showing that putting sunscreen on your skin would actually cause any damage.
To make it all more confusing, the EWG (Environmental Working Group) states on their website that a 2008 CDC (The Centers for Disease Control and Prevention) study detected oxybenzone in more than 96 percent of the American population (based on a representative sampling of children and adults) and that a 2016 study showed that adolescent boys with higher oxybenzone measurements had significantly lower total testosterone levels and recommends that consumers avoid sunscreens with oxybenzone. A good overview gives this table on EWG´s website that outlines human exposure and toxicity information for nine FDA-approved sunscreen chemicals.
When looking at the environment, there is another problem with oxybenzone. In 2015, Craig Downs, the executive director of the Haereticus Environmental Laboratory based in Clifford, Va., led a team that reported that oxybenzone is toxic to the symbiotic algae that live within corals, which provides their color and performs other vital duties, and also stunts the growth of corals. In 2008 the Environmental Health Perspectives published a study concluding that sunscreen promotes viral infection in corals that can lead to bleaching. They estimated that up to 14,000 tons of sunscreen is deposited in the world’s oceans each year. So it is important to check your sunscreen for for environmental friendliness by avoiding ones containing oxybenzone, octinoxate and methyl paraben. Haereticus Environmental Lab publishes a list of chemicals to avoid. Mineral sunblocks including zinc oxide and titanium dioxide that are “non-nano” in size are considered safe. Formulations below 100 nanometers are considered nano and can be ingested by corals. R. Scott Winters, the chief executive officer of the Coral Restoration Foundation, a nonprofit conservation organization based in Tavernier, Fl., stresses the importance of avoiding sunscreen with oxybenzone: "If we are to be successful in bringing coral reefs back to a healthy state, it is incredibly important that people visiting them choose sunscreens that do not contain oxybenzone. More important, choosing to cover up with UV protective clothing, rash guards, and hats can also reduce the amount of sunscreen needed." Hawaii recently banned sunscreens sunscreens containing chemicals believed to harm coral reefs. The legislation prohibits the distribution of sunscreens containing the chemicals oxybenzone and octinoxate that scientists have found contributes to coral bleaching when washed off in the ocean. When signed by the governor, the ban would go into effect January 1, 2021.
Another ingredient to look at is retinyl palmitate. Retinol and retinyl palmitate, both forms of vitamin A, are widely used ingredients in skin care products. Retinol is a pure form of the vitamin and retinal palmitate is considered to be a gentler, milder form of vitamin A. A combination of retinol and palmitic acid has been found to be an effective antioxidant, the reason why it is used in many sunscreens (the antioxidant protection helps prevent damage caused by UV rays). A 2009 study found that retinoic acid enhanced the photocarcinogenic activity of UVB rays in mice and increased multiplicities of skin lesions. Retinyl palmitate also enhanced photocarcinogenicity, increased skin lesions, and increased the presence of squamous cell neoplasm's: the beginnings of skin cancer. However, The American Academy of Dermatology defended the use of retinyl palmitate in sunscreen, stating there was “no convincing evidence” that the ingredient causes cancer. So, while there is still no conclusive answer as to whether retinyl palmitate is photocarcinogenic, products containing vitamin A (retinol and retinyl palmitate) increase cell turnover and exfoliation, leaving skin more susceptible to damage from UV rays.
So far we looked at the active ingredients in sunscreen, but inactive ingredients make up 50 to 70 percent of most sunscreen products. One ingredient in particular is a cause for concern: the preservative methylisothiazolinone. This ingredient can be found in many sunscreens, even ones marketed to children. Methylisothiazolinone is used alone or in mixtures with a related chemical preservative called methylchloroisothiazolinone. The American Contact Dermatitis Society named methylisothiazolinone its “allergen of the year” in 2013 and in 2015 the European Scientific Committee on Consumer Safety concluded that no concentration of Methylisothiazolinone (MI) could be considered safe in leave-on cosmetic products (it is still allowed in rinse-off products). In the US there is no ban on Methylisothiazolinone in leave-on products. Also, try to avoid spray-on sunscreens, because these can be inhaled.
In short, what should be avoided:
1. Sunscreens with the chemicals oxybenzone, avobenzone, octisalate, octocrylene, homosalate and octinoxate
2. Mineral sunscreens with nanoparticles
3. Spray-on sunscreens
If in doubt, you can check the list on EWG´s website.