Nanotechnology in Your Sunscreen: Doing More Harm than Good?

While soaking in the sunshine may feel good, and you may have heard about solar ultraviolet (UV) radiation harm, you may not be aware of what’s in your sunscreen. Lee Hong explored the benefits of sunscreen in his post on The Pipettepen, and today, we dive deeper into a smaller world – the nanotechnology in our sunscreen.

The two minerals available to sunscreen in form of nanosized particles (NPs) are zinc oxide (ZnO) and titanium dioxide (TiO2). They are less than 1/1000th the size of a human hair. Bulkier minerals in traditional sunscreen reflect visible light, making it opaque and cakey on your skin. NPs on the other side, scatter light instead of reflecting it, resulting in a disappearing and lighter feeling sunscreen.

https://www.flickr.com/photos/77654185@N07/14549162578/

Traditional sunscreens block out UV rays but many with ghostly white color. Nanotechnology make them disappear on your face!

While the resulting nanoproduct can be a big help, people have raised concerns over the safety of NPs-based cosmetic sunscreens. With their smaller size, NPs could in theory be absorbed into the skin at a higher level than their bulkier counterparts. The real question to ask is if these tiny particles are more harmful if absorbed, than good in protecting us from UV rays.

Studies are divided about whether NPs can pass through the skin. A few reassuring words from Paul Wright, a toxicology researcher at RMIT University, “There’s a negligible penetration of sunscreen particles,” as he told The Guardian, “They don’t get past the outermost dead layer of human skin cells.” In 2017, the Australian Therapeutic Goods Administration (TGA) published its review that NPs absorption is unlikely, based on both via in-vitro (i.e. studies using isolated skin cells) and in-vivo (i.e. studies on live skin tissue) studies. It appears that we are in a safe zone!

Other scientists have tested on the toxicity of these tiny metal oxides when exposed to UV light, simulating the real-life scenario for use of sunscreens. Their results indicated that the metal oxides may generate reactive free-radical species, leading to cancer due to DNA damage. However, this alarming impact on human health depends on whether NPs in sunscreen are absorbed into our skin. Providing some comfort, research associate Simon James at the Australian Synchrotron told to The Guardian that “Our study demonstrates that the human immune system has the right equipment to remove any nanoparticles that somehow make it through the skin, assuming some do at all.” Their work showed that human natural defenses can gather and destroy ZnO nanoparticles. Moreover, sunscreen manufacturers utilize surface coatings to improve transparent effect and as a result, the coated components can essentially reduce toxicity from lessen reactivity to UV lights.

https://www.flickr.com/photos/jimnix/7867453946/

It’s not a bad idea shielding your skin from burning sun with an umbrella’s shade whenever you are up for outdoor activities.

With the increased popularity of the nanotech-based products, another concern is noxious effects caused by inhalation of NPs. The Environmental Working Group (EWG), based out of Washington, D. C., announced a warning to refrain from spray sunscreen and loose powder cosmetics containing ZnO or TiO2 particles. The lungs have difficulty removing small particles and thus end up with organ damage possibly in the same way that air pollution is linked to lung cancer.

Evidence suggests there is more harm from skipping the sunscreen than exposing your skin to nanoparticles, but, if you’re not comfortable with these tiny oxides, UV protection umbrellas are another option!

Peer edited by Bailey DeBarmore.

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How’s that Nanoparticle Biocorona treating you??

No, sorry, it’s not the latest variety of Corona beer. Rather, it is a new exciting advance in understanding nanoparticle toxicity!

Nano-everywhere!

 ©2006 David Hawxhurst, Woodrow Wilson International Center for Scholars

Nanoparticles are found in lots of consumer products!

Nanoparticles are any really really small particles in the nanometer range (1-100 nanometers). For size comparison, the thickness of normal hair is 80,000 nanometers. Because they have different chemical and physical properties compared to larger particles, nanoparticles are already being used in numerous capacities. They are used to produce lightweight but strong materials for use in airplanes, in clothes to kill bacteria, in food packaging to promote shelf life, and in sunblock to improve UV protection. Much research is ongoing to include nanomaterials in medicine, such as to treat cancer and to improve medical imaging.

Though nanoparticles are becoming widely used in consumer products and there is increasing development of nanomedicine, our understanding of how nanoparticle exposure affects human health is struggling to keep up. Thus far, researchers thought that nanoparticle toxicity was dependent primarily on physical or chemical properties, like composition (silver vs. iron) or size. However, recent findings indicate that it might not be that simple.

The Biocorona

When nanoparticles come into contact with biological materials (for instance, the blood), proteins and other molecules are naturally attracted to its surface and begin to form layers around the nanoparticle. This biological coating is known as a biocorona. Thus, when the body is exposed to nanoparticles, it is likely encountering nanoparticles with a specific biocorona that has formed on it, not just the nanoparticle itself. Different biocoronas on the same type of nanoparticle can affect not only the particle’s chemical properties but also how it’s distributed throughout the body, how it’s eliminated from the body, and how the body reacts to it.

Dr. Jonathan Shannahan at Purdue University is one of many researchers trying to better understand how nanoparticles interact with the human body and the role of the biocorona in modifying toxicity.

Nanoparticle Meets Heart Disease

Recently, Dr. Shannahan’s team published a paper on how cardiovascular disease states can affect iron nanoparticle biocoronas and toxicity. Iron nanoparticles are being developed for use in medical imaging and cancer drug delivery, so it is important to better understand their potential toxic side effects in humans. Many of the current iron nanoparticle toxicity studies have been designed to represent how a healthy individual would react. However, 1 in 4 people in America die from cardiovascular disease each year and 31% of Americans have high levels of cholesterol in their blood, a high risk factor for cardiovascular disease. The toxicity studies we have now do not capture the effects of nanoparticles in a significant portion of the population, people with or at high risk of developing heart disease. These people may also use iron nanoparticle therapies and diagnostic tools so it is essential to study how people with these underlying disease states would react.

Courtesy of Dr. Jonathan Shannahan

Iron nanoparticles form different biocoronas when incubated with different kinds of serum (normal vs. hyperlipidemic) which generate different responses by the body.

To simulate normal and heart disease conditions in their experiment, Shannahan’s team incubated iron nanoparticles with blood serum from normal rats and rats with high blood levels of cholesterols (think LDL) and lipids, termed hyperlipidemic serum. They found that the nanoparticle biocorona changed when incubated in hyperlipidemic serum and that nanoparticles with a hyperlipidemic biocorona stimulated more of an immune response in cells that line the arteries! An increased immune response facilitates the formation of plaques in the arteries, which eventually could cause blockage of blood flow to the heart, leading to heart attacks.

Shannahan’s findings suggest that individuals with high blood cholesterol and/or heart disease may be more susceptible to the toxic effects of iron nanoparticles, i.e. they could have a worse reaction to iron nanoparticles than healthy individuals, and that this toxicity is driven by a change in the nanoparticle’s biocorona.

“King me.” – Nanoparticlenanoparticle

The discovery of this biological “crown” on nanoparticles and its ability to affect toxicity adds another piece to the complex puzzle of how to evaluate nanoparticle toxicity in humans. Such studies will only become more important as nanoparticles become more widely used in consumer products and, potentially, in modern medicine. Genetics, epigenetics, nutrition, environmental exposures, and now biocoronas will all play into the important quest to understand the toxicity of nanoparticles among the general population as well as for each individual.

Peer edited by Aminah Wali.

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