Sunscreen chemicals stay in the bloodstream for 24 hours, finds study

The ingredients are absorbed at a rate 40 times higher than previously known

Sunscreens are the most effective guard against UV damage and cancer.

Researchers have identified four chemicals, present in some standard sunscreens, that are absorbed by the skin and seep into the bloodstream at potentially dangerous levels. We say potentially because, while the amount of active ingredients was up to 40 times higher than the threshold approved by the FDA, it is unknown whether these chemicals cause or could cause any harm. In fact, the team behind the study urges people to continue using sunblock, calling it "the most preventable risk factor for developing skin cancer".

The study

The report was published in the Journal of the American Medical Association on May 6. For the study, four groups of participants were asked to apply various types of sunscreen products - two sprays, one lotion and one cream - four times a day for four days (the recommended amount). The blood samples collected after found that instead of simply sitting on the surface of the skin, all the sunscreens were getting absorbed at a level much higher than previously thought.

According to the FDA, any chemical that is absorbed at the rate of 0.5 nanograms per millilitre or less does not need safety testing, a category in which sunscreens were previously placed. This study, however, blows this theory to bits, with findings of more than 20ng/mL of some of the chemicals in the blood. These were also found to stay in the body for up to 24 hours.

To clarify, the researchers made it amply clear that just because they are being absorbed does not mean the chemicals are causing any harm, and that the ingredients have been used for several decades without any detrimental side effects so far.

The study does make it compulsory for these products and chemicals to undergo further testing, to find out more about their impact on human health.

The chemicals     

So what do we know about the four chemicals in question?

Avobenzone is an oil-soluble sun blocker, and protects the skin from UVA I, UVA II and UVB wavelengths.

Oxybenzone is an organic compound that absorbs UVB and UVA II rays.

Octocrylene is an oily liquid also used in cosmetics other than sunscreens, and absorbs UVB and short-wave UVA rays.

Ecamsule is a photostable compound that filters out UVA rays.

Not all sunscreens contain these four chemicals, with some products using zinc oxide and titanium dioxide instead. However, the rate of absorption of these products is not conclusively known, either, and could be less or more than the four listed above.

Having said that, it's worth noting that many activists are pushing to ban products made up of marine-life-harming oxybenzone and octinoxate. According to Lisa Bishop, president of the Friends of Hanauma Bay organisation: “When people put these two chemicals on and they come into the ocean, the product washes off and stays floating in the water, and the corals are being killed by it.”

Some eco-friendly brands include Colorescience, NYDG Skincare, La Roche-Posay, Dr Hauschka and Molecular Cosmetics, which carries photostable Sun Drops.

Sun Drops by Dr Barbara Sturm's Molecular Cosmetics

Even the most effective sunscreen is unlikely to offer full protection under the direct glare of the sun. It needs to be complemented by clothing, sunglasses, caps and umbrellas.